Congenital coronary sinus ostium atresia is a rare condition that is typically considered benign, as long as there is adequate drainage via another route. However, in children with single ventricle congenital heart disease, adequate drainage may not be assured after complex surgical interventions, putting them at risk for myocardial injury. We present a patient with complex single ventricle congenital heart disease who developed acquired coronary sinus ostium atresia after surgical intervention that was treated by a transcatheter approach to prevent the sequelae of coronary sinus hypertension. K E Y W O R D Scongenital heart disease,