Mantle Cell Lymphoma With Cardiac Involvement Presenting as Complete Heart Block.

A 50-year-old woman presented with complete heart block on electrocardiogram. Echocardiogram revealed an intracardiac mass with extensive cardiac involvement. The patient was diagnosed with mantle cell lymphoma, confirmed via lymph node biopsy. Pacemaker implantation and chemotherapy were initiated, with subsequent improvement noted. This showcases an unusual manifestation of intracardiac metastasis with conduction system infiltration.