Left atrial thrombus mistaken as a tumor after heart transplantation.

The occurrence of neoplastic malignancy due to chronic immunosuppression in heart transplant recipients is a well-known threat. Continuous check-ups are therefore mandatory in this patient group. We describe the case of a 58-year-old man transplanted for dilated cardiomyopathy. During regular diagnostic check-up, a solid mass in the left atrium was discovered on the transesophageal echocardiogram. Since the mass became progressively larger over three years and showed features of neither myxoma nor thrombus, a cardiac sarcoma was suspected. A secondary diagnostic magnetic resonance tomography (MRT) investigation was contraindicated due to an implanted pacemaker. Intraoperatively, the mass proved to be an organized thrombus. Surgery had to be performed without an established accurate diagnosis due to a suspected malignancy in chronically immunosuppressed patients.