Ablation of BAF250a, a critical regulatory subunit in the SWI/SNF BAF complex, in the SHF using Mef2c-Cre leads to persistent truncus arteriosus, trabeculation defects, reduced cardiomyocyte proliferation and differentiation, and embryonic lethality around E13, similar to our data from ablation of Brg1 with Isl1-Cre. Here, SMARCA4 is linked to Truncus arteriosus.