Abstract
3-Methylcrotonyl-CoA carboxylase (3-MCC) deficiency is a rare autosomal recessive disease of leucine catabolism. 3-MCC deficiency may lead to metabolic decompensation under stress; however, outcomes of elective surgery requiring cardiopulmonary bypass (CPB) are unknown. We report a 4-year-old girl with asymptomatic 3-MCC deficiency and atrial septal defect (ASD) who's undergone surgical ASD repair under CPB. She was otherwise normal developmentally and medically. Although patients with 3-MCC may face metabolic crises, the ASD repair under CPB was uneventful.