Thrombosis is a potential life-threatening complication in patients undergoing cardiac surgery. Various clinical and heritable conditions, like cancer, trauma, immobilization, the presence of factor V Leiden or prothrombin 20210A, deficiency of or resistance to the inhibitor proteins C, S, or antithrombin, elevated levels of coagulation proteins, antiphospholipid antibody syndrome, pregnancy, and the use of exogenous hormones, may contribute to catastrophic thrombosis. Massive thrombi with cerebrovascular and cardiovascular events develop in patients with polycythemia vera (PV). However, thrombus formation in the cardiac chambers is extremely rare. We report a case of massive intracardiac thrombosis in a patient undergoing coronary artery bypass grafting.