Geoffrey, a 7-year-old Thoroughbred gelding, presented to Cornell University's Hospital's Equine/Farm Animal Emergency Service on September 22, 2005 for further work-up of moderate colic of 7 days' duration. On presentation, cardiac auscultation revealed a grade II/VI systolic murmur on both left and right sides. Exploratory laparotomy was performed and ileocolic anastomosis performed. The patient experienced a protracted recovery from surgery. He remained persistently tachycardic and developed bilateral jugular vein thrombosis. Echocardiography was performed seven days post-operatively, revealing a vacuolated, heterogeneous mass attached to the endocardium of the right ventricle, measuring 19.6cm x 7.7cm. No blood flow was visualized within the mass and it was loosely attached to the endocardium, making the most likely etiology a thrombus. The mass extended into the right ventricular outflow tract resulting in obstruction of blood flow through the pulmonary artery, increased right ventricular pressure and tricuspid regurgitation. The objective of this case report is to discuss the hypercoagulative state that occurs in endotoxemic equine colic patients.