Coronary artery fistulas are rare, and the further development of mitral valvular insufficiency and endocarditis is even more uncommon. We report a case of endocarditis secondary to a congenital coronary artery fistula arising from the right coronary artery and draining into the left ventricle. Vegetations were found on the mitral valve leaflet. The fistula was successfully treated with surgery, and the endocarditis, with antibiotic therapy. Surgical repair is the optimal treatment for coronary artery fistula, even in asymptomatic patients.