We describe a rare case of native mitral valve thrombosis in a patient with rheumatic mitral valve disease without predisposing thrombophilia. The patient presented in heart failure with a new diagnosis of mitral stenosis. After a period of intravenous diuresis there was a sudden cardiovascular collapse. Trans-oesophageal echocardiogram identified an atrial mass obstructing the mitral valve. The patient proceeded to emergent mitral valve replacement. A coagulopathy was identified in the form of thrombus-induced disseminated intravascular coagulation (DIC). Mitral valve thrombosis is a rare cause of morbidity and mortality in rheumatic heart disease and is not readily identifiable on transthoracic echocardiography.