Hox genes define distinct progenitor sub-domains within the second heart field

► We reveal Hox gene expression in the second heart field (SHF). ► Expression of Hox genes in the SHF defines new cardiac progenitor sub-domains. ► Contribution of cardiac Hox-positive cells demonstrates pre-patterning of the SHF. ► Expression of Hox genes in the SHF depends on Retinoic Acid (RA) signaling. ► Cardiac contributions of Hox-positive SHF cells are RA sensitive.