Chromosome 4q deletion is one of the most frequently detected genomic imbalance events in congenital heart disease (CHD) patients. However, a portion of CHD-associated 4q deletions without known CHD genes suggests unknown CHD genes within these intervals. Here, we have shown that knockdown of SORBS2, a 4q interval gene, disrupted sarcomeric integrity of cardiomyocytes and caused reduced cardiomyocyte number in human embryonic stem cell differentiation model. Molecular analyses revealed decreased expression of second heart field (SHF) marker genes and impaired NOTCH and SHH signaling in SORBS2-knockdown cells. Exogenous SHH rescued SORBS2 knockdown-induced cardiomyocyte differentiation defects. Sorbs2^-/- mouse mutants had atrial septal hypoplasia/aplasia or double atrial septum (DAS) derived from impaired posterior SHF with a similar expression alteration. Rare SORBS2 variants were significantly enriched in a cohort of 300 CHD patients. Our findings indicate that SORBS2 is a regulator of SHF development and its variants contribute to CHD pathogenesis. The presence of DAS in Sorbs2^-/- hearts reveals the first molecular etiology of this rare anomaly linked to paradoxical thromboembolism.