The anomalous origin of the right coronary artery (ARCA) from the main pulmonary artery (MPA) is a rare congenital cardiac malformation and usually associated with other cardiac anomalies. Most patients with isolated ARCA from MPA remain asymptomatic, but they may develop myocardial ischemia and even sudden death. We reported an asymptomatic 7-year-old boy referred for evaluation of a heart murmur. Isolation of ARCA from MPA was diagnosed by echocardiography and then confirmed by cardiac catheterization and angiography. The right coronary artery was re-implanted into the ascending aorta. A preoperative thallium-201 myocardial perfusion showed a myocardial ischemia pattern in the anterolateral septal area after a dipyridamole stress test; the ischemia was completely resolved after surgery.