A sudden right-to-left shunt: the importance of evaluating patent foramen ovale during exercise.

A 55-year-old male affected by heart failure with reduced ejection fraction and a history of a transient cerebrovascular accident was accepted to the Cardiology Department for worsening dyspnea. A cardiopulmonary exercise test was performed after therapy optimization to further evaluate exercise intolerance. A rapid increase in the minute ventilation/carbon dioxide production slope, end-tidal oxygen pressure, and respiratory exchange ratio, with a concomitant decrease in end-tidal carbon dioxide pressure and oxygen saturation, were observed during the test. These findings indicate exercise-induced pulmonary hypertension leading to a right-to-left shunt. Subsequent echocardiography with a bubble test unveiled the presence of an unknown patent foramen ovale. It is, therefore, necessary to exclude a right-to-left shunt by cardiopulmonary exercise testing, particularly in patients predisposed to develop pulmonary hypertension during exercise. Indeed, this eventuality might potentially provoke severe cardiovascular embolisms. However, the patent foramen ovale closure in patients with heart failure with reduced ejection fraction is still debated because of its potential hemodynamic worsening.