Antiphospholipid syndrome has been associated with venous and arterial thrombotic events but intracardiac thrombosis is rare. We describe a case about a 30-year-old woman, admitted with a 6-month history of arthralgia, fatigue, and intermittent fever. Subsequent investigation revealed the presence of a large and calcified mass in the right ventricular outflow tract attached to the subvalvular tricuspid apparatus. Cardiac surgery was performed and histological examination demonstrated it to be composed entirely of calcified thrombus. Screening laboratory evaluation for hypercoagulable states confirmed the diagnosis of antiphospholipid syndrome.