We present a 71-year-old male, who had had a heart transplantation 24 years prior, who came to our clinic with a low-grade fever and a new II/VI holosystolic murmur. Echocardiography showed a large mass in the right atrium with attachment near the junction of the right atrium and superior vena cava. The patient was taken to the operating room for resection of the mass. Microscopic evaluation was consistent with thrombus. Differential diagnosis of cardiac masses after cardiac transplant includes tumour, thrombus, and vegetation. Final diagnosis can be challenging; multimodality imaging and biopsy or resection often are required for final diagnosis.