Coronary artery fistulae, being a rare form of congenital anomalies of the coronary arteries, are usually discovered by chance during coronary arteriography. However, these fistulae can cause an important coronary morbidity and mortality leading to angina, syncope, congestive heart failure, myocardial infarction and sudden death. The coincidence of mitral stenosis and congenital artery fistula is rare in the literature. In our case report, a patient with a coronary artery fistula originating from the circumflex, draining to the main pulmonary artery, discovered at cardiac catheterization and coronary angiography done with a prediagnosis of mitral stenosis is presented in the light of the literature.