Transcriptional activator that binds to the consensus sequence 5'-AGATAG-3' and plays a key role in cardiac development. In cooperation with TBX5, it binds to cardiac super-enhancers and promotes cardiomyocyte gene expression, while it down-regulates endocardial and endothelial gene expression. Involved in bone morphogenetic protein (BMP)-mediated induction of cardiac-specific gene expression. Binds to BMP response element (BMPRE) DNA sequences within cardiac activating regions. Acts as a transcriptional activator of ANF in cooperation with NKX2-5. Promotes cardiac myocyte enlargement. Required during testicular development. May play a role in sphingolipid signaling by regulating the expression of sphingosine-1-phosphate degrading enzyme, sphingosine-1-phosphate lyase. Interacts with ZNF260 (By similarity). Interacts with the homeobox domain of NKX2-5 through its C-terminal zinc finger. Also interacts with JARID2 which represses its ability to activate transcription of ANF. Interacts (via the second Zn finger) with NFATC4 (By similarity). Interacts with LMCD1 (By similarity). Forms a complex made of CDK9, CCNT1/cyclin-T1, EP300 and GATA4 that stimulates hypertrophy in cardiomyocytes. Interacts with NR5A1, ZFPM2 and TBX5. Interacts with TBX18. Methylation at Lys-300 attenuates transcriptional activity.