Malignant cardiac involvement is rare in patients with human T cell lymphotrophic virus type-1-associated adult T cell leukemia/lymphoma (ATLL). We report a single institution experience of eight patients with pathologically documented cardiac involvement with ATLL. Pericardial effusion and tamponade, cardiac valvular infiltration, valve leaflet tumor nodules and endocardial and myocardial tumors were observed. Cardiac involvement with ATLL was most often identified post-mortem; however, three cases were diagnosed clinically. All but one of the patients had the acute or lymphomatous subtypes of ATLL and had progressed through at least one prior systemic therapy. Patients with ATLL-related cardiac disease were also found to have pulmonary involvement suggesting that this may be a sign of increased risk of cardiac involvement. One patient with the chronic form of ATLL remains alive 10 years after undergoing cardiac valve replacement.