A 22 year old man developed symptoms of left ventricular failure secondary to atrial fibrillation and congenital mitral regurgitation. After operation for mitral valve repair he was unable to be successfully weaned from cardiopulmonary bypass and this was ascribed to poor left ventricular function. He therefore underwent emergency cardiac transplantation but again was unable to be weaned from bypass. At post-mortem examination a previously undiagnosed aortic coarctation was revealed. The presentation of occult aortic coarctation is discussed, and its association with congenital mitral valve abnormalities reviewed.