Postoperative survival for complete atrioventricular septal defect (cAVSD) is excellent. Common complications of surgery include valvular stenosis/regurgitation, left ventricular outflow tract obstruction, arrythmias, and residual defects. We report a challenging case of a 7-month old girl with Trisomy 21, preoperative obstructive sleep apnea with severe pulmonary hypertension, who underwent AVSD repair and required veno-arterial extracorporeal membrane oxygenation (V-A ECMO) while unable to come off cardiopulmonary bypass and developed left ventricular intramural hematoma during the course. This case highlights the challenges in management of an unusual complication.