Transcription factor required for the development of the heart and the spleen (PubMed:22560297). During heart development, acts as a transcriptional activator of NPPA/ANF in cooperation with GATA4 (By similarity). May cooperate with TBX2 to negatively modulate expression of NPPA/ANF in the atrioventricular canal (By similarity). Binds to the core DNA motif of NPPA promoter (PubMed:22849347, PubMed:26926761). Together with PBX1, required for spleen development through a mechanism that involves CDKN2B repression (PubMed:22560297). Homodimer (via the homeobox); binds DNA as homodimer (PubMed:22849347). Interacts (via the homeobox) with TBX5 (via the T-box); this complex binds DNA (PubMed:26926761). Interacts with HIPK1 and HIPK2, but not HIPK3. Interacts with the C-terminal zinc finger of GATA4 through its homeobox domain. Also interacts with JARID2 which represses its ability to activate transcription of ANF. Interacts with FBLIM1. Interacts with TBX18 (By similarity). Interacts with histone methyltransferase NSD2 (via HMG box) (By similarity). Expressed only in the heart. Expressed at embryonic stages 10 to 11 in the nondifferentiated mesodermal cells at the venous and arterial poles, as well as cells of the dorsal coelomic wall and ruptured mesocardium (at protein level) (PubMed:21403123). Expressed by all myocardial cells at embryonic stages 10 to 11 (at protein level) (PubMed:21403123). The homeobox domain binds to double-stranded DNA (PubMed:22849347). The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. Belongs to the NK-2 homeobox family.