Pulmonary and tricuspid valvuloplasty in carcinoid heart disease.

A 26-year-old female with carcinoid heart disease consisting of severe pulmonary and tricuspid valve stenosis was admitted with line associated sepsis. She recovered from sepsis with antibiotics and aggressive fluid resuscitation but became grossly volume overloaded with evidence of tense ascites and lower extremity edema. She developed worsening renal and hepatic function due to congestive nephropathy and hepatopathy, which did not respond to intravenous diuretics, and she was deemed too sick for surgical pulmonary and tricuspid valve replacement. Pulmonary and tricuspid valvuloplasty was performed as a rescue measure to alleviate her congestive symptoms and improve her candidacy for valve replacement. © 2016 Wiley Periodicals, Inc.

Noninvasive evaluation of right hemodynamics in carcinoid heart disease: A case report.

We report the case of a 67-year-old woman with a carcinoid tumor of midgut origin who developed carcinoid heart disease and died because of bowel perforation. Echocardiography allowed the diagnosis, recognizing the typical abnormalities of tricuspid and pulmonary valve leaflets. The sonographic examination also evidenced peculiar alterations of the right heart hemodynamics: end-diastolic reversal of flow at the level of the pulmonary valve, reduced respiratory excursion without enlargement of the inferior vena cava, and biphasic hepatic venous flow without respiratory variation. Echocardiography allowed both the diagnosis and the accurate assessment of the hemodynamic consequences of the disease. © 2016 Wiley Periodicals, Inc. J Clin Ultrasound 45:355-361, 2017.

Percutaneous balloon valvuloplasty in carcinoid pulmonary valve stenosis.

More than half of patients with carcinoid syndrome develop carcinoid valve disease. Both the tricuspid and pulmonary valve are often involved. Symptoms of carcinoid syndrome with flushing, diarrhea, and bronchospasm often precedes cardiac symptoms. We report a case of carcinoid initially presenting with rapid development of right heart failure due to severe pulmonary valve stenosis. In untreated carcinoid, there is a risk of carcinoid crisis with anesthesia and surgery. In local anesthesia, we performed a sub-acute balloon pulmonary valvuloplasty. The procedure was successful without any residual pulmonary valve stenosis and with immediately relief of dyspnea. The final diagnostic workup for the underlying malignancy continued the day after valvuloplasty. © 2015 Wiley Periodicals, Inc.

Results of Contemporary Valve Surgery in Patients with Carcinoid Heart Disease.

BACKGROUND: Carcinoid tumor is a slow-growing type of neuroendocrine tumor, originating from enterochromaffin cells and secreting mainly serotonin. The diagnosis is based on clinical symptoms, hormone blood levels, radiological and nuclear imaging, and histological confirmation. However, most patients have metastases at the time of diagnosis because the clinical signs often remain unnoticed or are attributed to other abdominal conditions. In up to 50% of patients the endocardium is affected due to a hormonally active tumor profile. The study aim was to report the outcome of surgical treatment in patients with carcinoid heart disease, including the data of radiological and nuclear imaging, histological diagnosis, and follow up information. METHODS: Between 2008 and 2014, a total of 39 consecutive patients (28 males, 11 females; mean age 66 years; range: 28-84 years) with carcinoid heart syndrome were operated on at the authors' institution. Valvular heart disease was diagnosed with two-dimensional echocardiography. The study population included 26 patients (67%) with severe metastatic disease, who underwent radiotherapy preoperatively, and 13 patients (33%) who were metastasis-free and did not receive preoperative systemic therapy. Follow up was available for all hospital survivors, all of whom underwent serial echocardiographic follow up postoperatively. Adverse cardiac events were defined as cardiac-related death, a need for valvular reintervention, the occurrence of valve prosthesis-related complications, or echocardiographic evidence of new, high-degree valvular dysfunction during follow up. RESULTS: The majority of patients (n = 34; 87%) underwent isolated tricuspid valve replacement, while simultaneous pulmonary valve replacement was performed in five patients (13%). Postoperative complications included reoperation for bleeding in five patients (13%) and new heart block requiring pacemaker implantation in 10 (25%). The in-hospital mortality was 5% (n = 2). The overall survival was 43% at six years postoperatively. At the latest follow up, 12 of the 17 survivors were in NYHA class I, and five in NYHA class II. The adverse cardiac event rate was 71%. Echocardiographically, 46% of patients (6/13) showed at least stationary or mild improvement in the right ventricular ejection fraction at follow up, with no evidence of paravalvular leak, infective endocarditis, or progressive other native valvular carcinoid affection. Postoperatively, the right atrial dimensions were preserved as normal in 23 patients (59%), mildly dilated in six (15%), moderately dilated in three (8%), and severely dilated in seven (18%). Valve-in-valve transcatheter aortic valve implantation was performed in two patients (12%) due to structural degeneration of the valve bioprosthesis and native valve disease progression. CONCLUSIONS: Despite advanced systemic disease, the surgical treatment of patients with carcinoid heart syndrome is associated with an acceptable perioperative risk and satisfactory mid-term survival. Those patients who survived valve surgery benefited from a significant improvement in their functional capacity. Percutaneous procedures may represent a useful tool to reduce the risk of late valvular reinterventions.

Valve Replacement in Patients with Carcinoid Heart Disease: Choosing the Right Valve at the Right Time.

BACKGROUND AND AIM OF THE STUDY: The prosthetic valve of choice in patients with carcinoid valve disease (CVD) remains controversial due to the limited life expectancy of patients with advanced-stage neuroendocrine tumors (NETs) on the one hand, and concerns regarding structural valve deterioration (SVD) on the other hand. METHODS: The records of 17 patients (11 females, seven males; mean age 65 ± 11 years; undergoing 18 operations) with primarily right heart failure due to CVD were reviewed. All patients received somatostatin analogs perioperatively. Hospital and follow up data (acquired via direct patient contact and echocardiography) collected included baseline characteristics, procedural details, and clinical outcomes. RESULTS: The primary NET site was the ileum (n = 11), lungs (n = 2) and stomach, colon and appendix (n = 1 each). In one patient the primary tumor location could not be identified. Preoperative urinary levels of 5-hydroxyindole acetic acid (5-HIAA; 61 ± 36 mg/24 h) and serum levels of chromogranin A (2926 ± 4057 ng/ml) were 10- and 50-fold greater than normal, respectively. A total of 23 valves was implanted: five tricuspid valve replacements (TVR; four tissue and one mechanical), TVR and pulmonary valve replacements (PVR; three tissue and one mechanical), and TVR and mitral valve replacements (MVR; one tissue and two mechanical). The 30-day mortality was 11% (n = 2). No patient experienced a carcinoid crisis. The mean follow up was 24 ± 21 months (range: 4-85 months). Four patients (receiving seven valves) developed SVD at 12, 14, 15, and 20 months after surgery, and all of these patients died. The actuarial four-year survival and freedom from SVD were 23 ± 14% and 43 ± 15%, respectively. CONCLUSIONS: The data acquired suggested that the main advantage of tissue valve prostheses, namely to avoid lifelong, intense anticoagulation, might be offset by accelerated SVD. The use of mechanical valves should be considered in CVD patients with a large primary tumor mass and persistent high urinary levels of 5-HIAA, and who are unresponsive to therapy.

Carcinoid Heart Disease: From Pathophysiology to Treatment--'Something in the Way It Moves'.

Carcinoid heart disease (CHD) is a rare cardiac manifestation occurring in patients with advanced neuroendocrine tumours and the carcinoid syndrome, usually involving the right-sided heart valves and eventually leading to right heart failure. The pathophysiology of CHD is still obscure and believed to be multifactorial, as a variety of vasoactive substances secreted by the tumour appear to be involved. The management of patients with CHD is complex, as both the systemic malignant disease and the heart involvement have to be addressed. Timely diagnosis and early surgical treatment in appropriately selected patients are of outmost importance, as CHD is associated with increased morbidity and mortality. Valve replacement surgery alleviates right heart failure and may also contribute to improved survival. In the present study we have comprehensively reviewed the existing literature to date, mainly focusing on the pathophysiology of CHD. Other aspects of CHD (such as the clinical presentation, diagnostic tools and therapeutic approach) are addressed in brief.

Carcinoid Heart Valve Disease: Transcatheter Pulmonary Valve-In-Valve Implantation in Failing Biological Xenografts.

BACKGROUND AND AIM OF THE STUDY: Carcinoid heart valve disease (CHVD) occurs as the cardiac manifestation of carcinoid syndrome (also known as Hedinger's syndrome), which develops secondary to neuroendocrine tumor activity. CHVD almost exclusively affects right-sided heart valves, since circulating serotonin is metabolized by pulmonary endothelial cells, thus sparing left-sided valves. Replacement of the tricuspid and pulmonary valve is a well-established and feasible therapeutic option for these patients. Whether biological valve substitutes are subject to a continuous degenerative process is not entirely clear at present due to the rarity of the disease and inconclusive findings in the current literature. METHODS: Herein are presented the details of two patients suffering from advanced CHVD who had undergone previous combined tricuspid valve replacement (TVR) and pulmonary valve replacement (PVR) using biological xenografts, and had subsequently been readmitted with failure of the pulmonary valve substitute. RESULTS: Due to the increased risk for repeat surgical valve replacement, the patients were treated by percutaneous stent implantation into the pulmonary artery, followed by the implantation of a balloon- expandable transcatheter heart valve (THV). The procedures were feasible and safe through the intact TVR. CONCLUSION: This strategy resulted in a favorable acute outcome in both patients, with adequate valve function and no PVL as documented by TTE, although the transvalvular gradients were elevated in both cases. The patients had an uneventful postoperative course and were discharged home in timely fashion. Whether the residual elevated transvalvular gradients following the valve-in-valve procedures, or an early degeneration of the implanted bioprostheses, will have a negative impact on the patients' further course will become clear in the future.

Circulating plasma and platelet 5-hydroxytryptamine in carcinoid heart disease: a pilot study.

BACKGROUND AND AIM OF THE STUDY: Carcinoid heart disease (CaHD) is a rare form of valvular heart disease in patients with carcinoid syndrome (CS). The role of 5-hydroxytryptamine (5-HT) in the pathogenesis of CaHD is unclear. The study aim was to evaluate the association between platelet 5-HT (5-HTplt) and plasma 5-HT (5-HTpls) and valvular dysfunction. METHODS: Twelve patients with CaHD, 18 with CS and 10 'normal' subjects were recruited. Patients with CaHD underwent cardiac catheterization and echocardiography. 5-HTplt and 5-HTpls was sampled in blood from the femoral vein, right and left ventricle, and left antecubital fossa vein. RESULTS: Levels of 5-HTpls and 5-HTplt were significantly higher in patients with CaHD (median 5-HTpls 325 nmol/l and 5-HTplt 18.9 nmol/10(9) platelets) and CS (median 5-HTpls 155 nmol/l and 5-HTplt 16.4 nmol/10(9) platelets) when compared to healthy controls (median 5-HTpls 9 nmol/l and 5-HTplt 3.7 nmol/10(9) platelets; p < 0.0001 and p = 0.003, respectively). There was a significant increase in 5-HTplt and 5-HTpls between the femoral vein and right heart (p = 0.007 and p = 0.0002, respectively). There was no significant difference in 5-HTplt or 5-HTpls between the right and left side of the heart, irrespective of the presence of a patent foramen ovale or of left-sided CaHD. CONCLUSION: Plasma and platelet 5-HT levels are elevated in patients with CaHD. Despite exposure to similar levels of intracardiac plasma and platelet 5-HT, the development of valve dysfunction is heterogeneous. This suggests that individual heart valves have a susceptibility to the development of valvular dysfunction which is not related solely to plasma or platelet 5-HT levels.

Occurrence of left-sided heart valve involvement before right-sided heart valve involvement in carcinoid heart disease.

Carcinoids are rare neuroendocrine tumours that occur primarily in the gastrointestinal tract. Carcinoid heart disease is characterized by fibrous plaque deposition on the endocardial surface of the cardiac valves and chambers. It affects the right heart valves in 85% of cases and the left heart valves in 15%. We present an unusual case of a patient with metastatic carcinoid heart disease in whom typical carcinoid aortic and mitral valve lesions developed 2 years prior to the development of severe right-sided carcinoid valvular heart disease.

Outcomes and periprocedural management of cardiac implantable electronic devices in patients with carcinoid heart disease.

BACKGROUND: Carcinoid heart disease (CHD) is a rare complication of hormonally active neuroendocrine tumors that often requires surgical intervention. Data on cardiac implantable electronic device (CIED) implantation in patients with CHD are limited. OBJECTIVE: The purpose of this study was to evaluate the experience of CIED implantation in patients with CHD. METHODS: Patients with a diagnosis of CHD and a CIED procedure from January 1, 1995, through June 1, 2020, were identified using a Mayo Clinic proprietary data retrieval tool. Retrospective review was performed to extract relevant data, which included indications for implant, procedural details, complications, and mortality. RESULTS: A total of 27 patients (55.6% male; mean age at device implant 65.6 ± 8.8 years) with cumulative follow-up of 75 patient-years (median 1.1 years; interquartile range 0.4-4.6 years) were included for analysis. The majority of implanted devices were dual-chamber permanent pacemakers (63%). Among all CHD patients who underwent any cardiac surgery, the incidence of CIED implantation was 12%. The most common indication for implantation was high-grade heart block (66.7%). Device implant complication rates were modest (14.8%). No patient suffered carcinoid crisis during implantation, and there was no periimplant mortality. Median time from implant to death was 2.5 years, with 1-year mortality of 15%. CONCLUSION: CHD is a morbid condition, and surgical valve intervention carries associated risks, particularly a high requirement for postoperative pacing needs. Our data suggest that CIED implantation can be performed relatively safely. Clinicians must be aware of the relevant carcinoid physiology and take appropriate precautions to mitigate risks.

Features of carcinoid heart disease identified by cardiac computed tomography.

BACKGROUND: Carcinoid heart disease (HD) is a rare form of valvular heart disease, the features of which have not been fully described by cardiac computed tomography (CT). METHODS: All patients with carcinoid HD that underwent cardiac CT, either preoperatively or for assessment of coronary arteries, between Apr-2006 and Dec-2019 at the Royal Free Hospital, UK, were reviewed. RESULTS: Of 32 patients with carcinoid HD, 29 (91%) had heart valve involvement. Abnormalities of the tricuspid and pulmonary valves were present in all patients, affecting all three leaflets in 23/26 (89%) unoperated patients for both valves. The aortic valve was affected in 4/29 (14%) patients and the mitral valve in 5/29 (17%). Left heart valves were affected in 6/29 (21%) patients. One patient (1/29; 3%) had all four valves affected. Severe changes with significant valvular regurgitation were seen in ≥75% of patients with tricuspid, pulmonary, and aortic valve abnormalities. Three patients had carcinoid myocardial metastases (3/32; 9%) and one patient had constrictive pericarditis (1/32; 3%). Ten patients had surgery of whom four (40%) had invasive coronary angiography preoperatively. Ten patients had a patent foramen ovale. Cardiac CT allowed an accurate assessment of damage to different leaflets/cusps, particularly of the pulmonary valve, where visualization with echocardiography was often (3/8; 38%) incomplete. CONCLUSION: Cardiac CT is a powerful tool for assessment of cardiac valve abnormalities, coronary arteries and the spatial relationship of coronary arteries with myocardial metastasis in patients with carcinoid HD, and should form part of multimodal imaging of this complex pathology.

Carcinoid Heart Disease: Review of Current Knowledge.

Carcinoid heart disease is the collective term for all cardiac manifestations in patients who have carcinoid syndrome. Carcinoid heart disease has a multifactorial pathophysiology, and the right side of the heart is usually involved. Symptoms and signs vary depending upon the affected cardiac components; most typical is right-sided heart failure secondary to diseased tricuspid and pulmonary valves. Despite no single ideal diagnostic test, strong suspicion, coupled with serologic and imaging results, usually enables diagnosis. Advances in imaging, such as speckle-tracking echocardiography and cardiac magnetic resonance, have improved the diagnostic yield. Treatment is challenging, warrants a multidisciplinary approach, and can be medical or surgical depending on the cardiac manifestations. Investigators are exploring the therapeutic use of monoclonal antibodies and new somatostatin analogues. In this review, we cover current knowledge about the pathophysiology, diagnosis, and treatment of carcinoid heart disease.

The path to surgery in carcinoid heart disease: a retrospective study and a multidisciplinary proposal of a new algorithm.

Background: Development of carcinoid heart disease (CHD) is the major negative prognostic factor in patients with the carcinoid syndrome. The only effective treatment is valve replacement. However, the selection of candidates and determination of optimal timing remain unclear. Considerable variability in local screening and treatment strategies exist. Methods: In this single-centre study, we retrospectively analysed the diagnostic process and outcome of all CHD patients who underwent valve surgery between 2000 and 2016. We propose a new CHD screening and management algorithm. Results: All patients (n = 15), mean age 64 ± 7, underwent tricuspid valve surgery. In 14 of them (93%) an additional valve was replaced. In only a minority of patients (27%) CHD diagnosis was established by screening. Survival after 1, 3, 12 and 24 months was 93%, 80%, 53% and 33%, respectively. Causes of death included infections and critical illness immediately postoperatively, and tumour progression and right heart failure in the longer term. There was a trend (p = .099) towards better preoperative right ventricular function in the patients who survived more than 12 months postoperatively (TAPSE 20 mm ± 4) compared to those who died between 3 to 12 months after surgery (TAPSE 16 mm ± 1). The former group had a shorter mean interval from diagnosis of the carcinoid syndrome to cardiac diagnosis than the latter (13 vs. 105 months, p = .014). Conclusion: Mortality after valve replacement for CHD remains high. A probably underestimated cause is late referral for cardiac surgery. We propose a systematic, multidisciplinary approach to all carcinoid syndrome patients.

Improving outcome of valve replacement for carcinoid heart disease.

OBJECTIVE: Carcinoid heart disease is characterized by tricuspid valve regurgitation and varying degrees of pulmonary valve regurgitation or stenosis. Valve replacement procedures may be complicated by systemic effects of carcinoid syndrome, as well as hepatic dysfunction and right heart failure. This study was performed to identify factors that might be associated with improving early mortality rates and late outcomes. METHODS: Between November 1985 and January 2018, 240 adult patients underwent surgery for carcinoid heart disease at the Mayo Clinic. We analyzed the association of multiple clinical and echocardiographic variables on early mortality and late survival. RESULTS: The median (interquartile range) age of patients was 63 years (55-69), and 117 patients (49%) were male. Before operation, 157 patients (70%) had New York Heart Association class III or IV limitation. Somatostatin analogs were used in 221 patients (92%), and long-acting somatostatins were used in 130 patients (54%). Loop diuretic therapy was used preoperatively in 125 patients (52%). Early mortality rate was 29% (9/22) between 1985 and 1994, but decreased to 7% (6/81) during 1995 to 2004, and to 5% (7/128) from 2005 onward. Overall survival estimates at 1, 3, and 5 years were 69%, 48%, and 34%, respectively. Older age, advanced New York Heart Association class, and a nonlinear effect of creatinine were independently associated with overall mortality. CONCLUSIONS: Valve replacement for carcinoid heart disease has acceptable short-term mortality, and early risk has decreased in the current era. Earlier intervention may improve overall survival.

Cases in a series of carcinoid syndrome and carcinoid heart disease.

Although carcinoid syndrome is regarded as a rare entity, carcinoid patients with evidence of cardiac involvement show a markedly reduced survival time. Patients with advanced signs of right-sided heart failure represent a subgroup at particularly high risk. Echocardiography remains the gold standard to diagnose or confirm structural cardiac involvement in patients with underlying carcinoid disease. This is the notion that propelled us to report on cases of carcinoid syndrome with cardiac involvement. We also review carcinoid syndrome and carcinoid heart disease, and challenges regarding the diagnosis and management of carcinoid heart disease.

Exercise cardiac magnetic resonance imaging with pulmonary artery catheter monitoring in carcinoid heart disease: a shift towards early intervention?

Neuroendocrine tumours are a rare malignancy, which can be complicated by a carcinoid syndrome and, in more rare cases, also valve destruction. The correct timing for surgical repair remains unknown. We report the first-in-men exercise cardiac magnetic resonance imaging with pulmonary artery catheter measurements in order to better understand the haemodynamic impact of isolated tricuspid valve insufficiency in a low symptomatic patient. Not pressure but volume overload is the key factor in the development of symptoms, as long as the right ventricular function is intact. Based on our findings, we referred the patient for tricuspid valve replacement. This case, together with the review of all carcinoid heart disease cases in our hospital (a large tertiary cardiology and oncology centre) since 2000, indicates a potential benefit for early intervention in carcinoid heart disease.

Carcinoid syndrome: update on the pathophysiology and treatment.

Approximately 30-40% of patients with well-differentiated neuroendocrine tumors present with carcinoid syndrome, which is a paraneoplastic syndrome associated with the secretion of several humoral factors. Carcinoid syndrome significantly and negatively affects patients' quality of life; increases costs compared with the costs of nonfunctioning neuroendocrine tumors; and results in changes in patients' lifestyle, such as diet, work, physical activity and social life. For several decades, patients with neuroendocrine tumors and carcinoid syndrome have been treated with somatostatin analogues as the first-line treatment. While these agents provide significant relief from carcinoid syndrome symptoms, there is inevitable clinical progression, and new therapeutic interventions are needed. More than 40 substances have been identified as being potentially related to carcinoid syndrome; however, their individual contributions in triggering different carcinoid symptoms or complications, such as carcinoid heart disease, remain unclear. These substances include serotonin (5-HT), which appears to be the primary marker associated with the syndrome, as well as histamine, kallikrein, prostaglandins, and tachykinins. Given the complexity involving the origin, diagnosis and management of patients with carcinoid syndrome, we have undertaken a comprehensive review to update information about the pathophysiology, diagnostic tools and treatment sequence of this syndrome, which currently comprises a multidisciplinary approach.

Carcinoid heart disease revealed by cyanosis with both right and left valvular involvement: a case report.

BACKGROUND: Carcinoid heart disease is a frequent complication of carcinoid syndrome. It is related to the release by the carcinoid tumor and/or its metastases of bioactive substances such as serotonin. It is characterized by right-sided valvular involvement and can lead to right-sided heart failure. It is a prognostic factor of carcinoid syndrome. CASE PRESENTATION: We report the case of a 53-year-old African woman with an endocrine tumor of her small intestine complicated by carcinoid heart disease, revealed by right-sided heart failure. The diagnosis was confirmed by transthoracic echocardiography, which showed a severe tricuspid regurgitation with a patent foramen ovale, and by increased serum chromogranin A and urinary 5-hydroxyindoleacetic acid. Initially she was treated with medical therapy (furosemide and injection of somatostatin). Afterwards she was proposed for surgery. The evolution of her treatment was good. CONCLUSIONS: Carcinoid syndrome is complicated in 60% of the cases of a heart disease, and is responsible for an important morbidity and mortality. The prognosis of patients with carcinoid heart disease has improved in recent years through somatostatin analogues and the cardiac surgery.

Long-term serotonin effects in the rat are prevented by terguride.

Long-term hyperserotoninemia induces heart valve disease in rats, and cases of cardiac valvulopathies have been reported in patients using ergolines, possibly through activation of the 5-hydroxytryptamine(2B) (5HT(2B)) receptor. The ergoline terguride (transdihydrolisuride) is a 5HT(2B/2C) receptor antagonist. Using a rat model, we have investigated whether terguride could prevent serotonin-induced changes in general and heart disease specifically. During 4 months, twelve Sprague-Dawley rats were given daily subcutaneous serotonin injections; twelve rats received a combination of serotonin injections and terguride by gavage, whereas ten rats were untreated controls. Using echocardiography, rats with aortic insufficiency were found in all 3 groups, while pulmonary insufficiency was only found in two rats injected with serotonin alone. Animals given serotonin alone had significantly higher heart weights compared to the controls (p=0.029) and rats given terguride (p=0.034). Rats injected with serotonin alone developed macroscopic skin changes at the injection sites, histologically identified as orthokeratosis and acanthosis. Terguride completely prevented these changes (p=0.0001, p=0.0003). Liver weights were higher in the animals given serotonin alone compared to controls (p=0.014) and terguride treated animals (p=0.009). Stomach weights were higher in animals given serotonin alone compared to rats given terguride (p=0.012). In the mesenchymal cell-line MC3T3-E1, terguride almost completely inhibited serotonin-induced proliferation (p<0.01). Serotonin increases heart, liver and stomach weights, possibly through enhanced proliferation. Terguride inhibits these effects. We propose that terguride may have beneficial effects in the treatment of diseases such as carcinoid syndrome, where serotonin plays an important pathogenic role.

Long-term serotonin administration induces heart valve disease in rats.

BACKGROUND: The purpose of this study was to investigate whether rats dosed with serotonin develop changes similar to those seen in human carcinoid heart disease. METHODS AND RESULTS: Ten Sprague-Dawley rats were given serotonin injections subcutaneously once daily for 3 months; controls were given saline. A long-lasting hyperserotoninemia with a >10-fold increase in both platelet-poor plasma and dialysate from the femoral muscles appeared. The animals developed clinical signs such as flushing and loose stools. After 3 months, 6 of 10 rats given serotonin had pathological echocardiographs. Two animals had a combination of aortic and pulmonary valve insufficiency, 1 had isolated aortic valve insufficiency, and 3 had isolated pulmonary valve insufficiency. Histopathological examination revealed shortened and thickened aortic cusps and carcinoidlike plaques characterized by a collection of myofibroblasts within an extracellular matrix of collagen ground substance. Immunostaining for Ki-67 demonstrated an increased number of proliferating subendocardial cells. In the control group, no pathological changes were seen. With the use of reverse-transcription polymerase chain reaction, normal rat aortic cusps were shown to express mRNA for serotonin receptors 5-HT1A, 5-HT2A, and 5-HT2B and the serotonin transporter 5-HTT. CONCLUSIONS: For the first time, long-term serotonin administration was performed in rats. Morphological and echocardiographic changes similar to those seen in human carcinoid heart disease developed. This study demonstrates that serotonin most likely is involved in the pathogenesis of carcinoid heart disease.