A case of a 66-year-old patient 13 years after coronary artery bypass grafting (CABG) admitted to hospital with typical ischemic chest pain and symptoms of superior vena cava syndrome (SVCS) is described. Non-invasive diagnostics confirmed acute coronary syndrome: non-ST-elevated myocardial infarction (ACS NSTEMI). Trans-thoracic echocardiography (TTE) revealed a gigantic tumor mass modeling the right atrium, causing chronic cardiac tamponade. Angiography showed that the tumor mass was in fact the aneurysmatically changed venous bypass graft to the right coronary artery (RCA). Computed tomography angiography (CT-angio) confirmed venous aneurysm size (the longest diameters were 10.2 cm × 8.7 cm). We also present treatment planning and the aneurysmal surgical removal procedure of this very rare case.