Congenital left ventricular diverticulum is a rare cardiac anomaly. During the newborn period, symptomatic patients are diagnosed with heart failure findings. We present a 23-day-old male newborn with congenital left ventricular diverticulum diagnosed during fetal echocardiographic examination. After the birth, the patient had heart failure symptoms and his echocardiographic examination showed low cardiac ejection fraction. Diverticulum was operated with endoventricular circular patch plasty (DOR) technique, and after, cardiopulmonary bypass venoarterial extracorporeal membrane oxygenation (ECMO) support was performed because of low cardiac output syndrome. On postoperative day 17, he was discharged with no problem.