Abstract Clarification of the mechanisms of cardiac-specific gene expression provides not only basic knowledge about how the gene expression is regulated in the heart, but also about the changes in the gene expression during the development of cardiovascular diseases. The purpose of this study was to analyze the mechanisms of cardiac chamber-specific gene expression and cardiac gene activation induced by mechanical load. In the present study, the experiments were carried out by using two cardiac genes, salmon cardiac peptide (sCP) and rat B-type natriuretic peptide (BNP) genes as models. sCP was discovered previously in our laboratory and turned out to be extremely cardiac-specific, representing A-type natriuretic peptide characters in an exaggerated way. In neonatal rat cardiomyocytes, the sCP promoter activity was shown to be strictly restricted to atrial cells and the promoter to be inert to cardiac hypertrophy-inducing factors. In order to find out the mechanisms of earlier proved BNP gene activation by mechanical load, BNP promoter activity was studied in vivo in adult rat hearts. The tandem GATA transcription factor binding site at position -80/-91 was shown to be essential for the BNP gene induction by angiotensin II. To clarify the possiblity to transfer the characters of the BNP gene into the sCP gene, short BNP fragments were inserted to the sCP gene promoter. The otherwise atrial-restricted sCP promoter was shown to be switched on in rat ventricular cardiomyocytes by adding a short BNP proximal promoter element to the sCP promoter, preferably near to the transcription start site. This activity was partly dependent on the -80/-91 GATA sites in the BNP promoter. Thus, A-type natriuretic peptide regulation can be switched to B-type regulation by a short proximal BNP promoter element. In conclusion, these studies reveal certain basic differences in cardiac atrial and ventricular gene expression.