coronary arteriovenous fistula, an unusual congenital abnormality characterized by a direct communication between a coronary artery, usually the right, and the right atrium or ventricle, the coronary sinus, or the vena cava. There may be a left-to-right shunt of small magnitude causing no symptoms, but a large shunt may result in growth failure, limited exercise tolerance, dyspnea, and anginal pain. Possible complications of a large shunt are bacterial endocarditis, rupture of an aneurysmal fistula, thrombus formation that causes occlusion or distal embolization, and in rare cases pulmonary hypertension and congestive heart failure. A loud continuous murmur heard at the lower or midsternal border of the heart suggests a coronary arteriovenous fistula; the diagnosis may be confirmed by coronary arteriography or aortography. Closure of the fistulous tract is a safe surgical procedure with excellent long-term results.
