Optimal management of muscular ventricular septal defects (MVSDs) remains controversial. Left ventriculotomy is the cornerstone of surgical repair but is frequently complicated by residual shunts, left ventricular dysfunction, apical aneurysm, or arrhythmias. In this study, we evaluated the long-term outcomes of surgical repairs in infants with isolated MVSDs. We retrospectively analyzed clinical data from 56 children with MVSDs (31 males, 25 females). Follow-up by questionnaire and Doppler echocardiography was performed at discharge and between 2 and 124 months after surgery. Patient age was 2 to 40 months (median, 21 months) and weight was 3.0 to 15.3 kg (median, 5.3 kg). Two patients died after surgery (hospital mortality, 3.57%). One patient with MVSDs died of low cardiac output caused by the long duration of cardiopulmonary bypass. Another patient with Swiss cheese MVSD received a single patch closure but died of low cardiac output immediately after cardiopulmonary bypass. Immediate complications such as a third-degree atrial-ventriclar block occurred in 2 patients, but they recovered before discharge and showed no residual shunt. No deaths occurred during follow-up, but a residual shunt was found in 1 patient. Delayed complete heart block requiring a pacemaker occurred in 1 patient. One patient showed paroxysmal supraventricular tachycardia that was treated with amiodarone. The left ventricular ejection fraction was 0.45-0.55 in 8 patients and 0.55-0.73 in 46 patients. No apical aneurysm was found. All the surviving patients returned to normal school life. Our results indicate that surgery is a suitable treatment option in infants and children with isolated MVSDs and that preoperative diagnosis is crucial to a successful outcome. Infants can tolerate a left ventriculotomy incision for MVSDs in the lower or apical ventricular septum.