A premature infant with a large patent ductus arteriosus and mild supravalvular aortic stenosis had evidence of severe myocardial ischemia after ductus ligation. Urgent reoperation was required to relieve severe obstruction of the left coronary orifice and the supravalvular stenosis was repaired. This unusual presentation early in infancy emphasizes that left coronary artery obstruction should be suspected even in the presence of mild supravalvular stenosis.