The function of NKX2-5 (NK2 homeobox 5, ENSG00000183072) is as follows. 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). Positively regulates transcription of genes such as COL3A1 and MMP2, resulting in increased pulmonary endothelial fibrosis in response to hypoxia (PubMed:29899023). {ECO:0000250|UniProtKB:P42582, ECO:0000269|PubMed:22560297, ECO:0000269|PubMed:22849347, ECO:0000269|PubMed:26926761, ECO:0000269|PubMed:29899023}.