What is the underlying cause of this pregnant patient's murmur? A pregnant woman in her 30s was found to have a systolic murmur. Transthoracic echocardiogram showed a mean gradient of 72 mm Hg across the left ventricular outflow tract. Cardiac computed tomography demonstrated supravalvular aortic stenosis with an hourglass appearance at the sinotubular junction (Figure, A), diffuse coronary ectasia with a distal left main aneurysm (Figure, B), ascending aorta and arch hypoplasia, and pulmonary artery stenosis. These findings suggested Williams syndrome, a genetic disorder in which coronary dilatation and thoracic vascular stenoses coexist. The dilatation is attributable to persistently high pressure that the coronaries are subjected to by left ventricular ejection into a small aorta, and the stenoses are because of a lack of elastin.1 A woman who is pregnant and asymptomatic with severe supravalvular aortic stenosis is at risk of heart failure, and management at a referral center is recommended.2 This patient, who had a history of cesarean delivery, underwent a repeated, unremarkable cesarean delivery, and an aortic hemiarch replacement is planned.