Platelet-derived growth factor (PDGF) is a dimeric molecule consisting of disulfide-bonded A- and B-polypeptide chains. Homodimeric (PDGF-AA, PDGF-BB) as well as heterodimeric (PDGF-AB) isoforms exert their effects on target cells by binding with different specificities to two structurally related protein tyrosine kinase receptors, denoted alpha- and beta-receptors. PDGF stimulates growth in various cell types, but little is known about its effect on mammalian cardiomyocytes. Therefore, growth-promoting effect of PDGF on rat cardiomyocytes was investigated. Primary culture of neonatal rat ventricular myocytes was prepared and cellular growth was estimated by [3H]-leucine incorporation assay. Tyrosine-phosphorylated PDGF-beta receptor of cardiomyocytes was determined by immunoblotting analysis after immunoprecipitation. PDGF-beta receptor, extracellular signal-regulated kinase (ERK) 1/2 and phosphorylated ERK1/2 of cardiomyocytes were measured by immunoblotting analysis. [3H]-leucine incorporation into the cultured myocytes was increased in a time- and dose-dependent manner after PDGF-BB stimulation. Phosphorylation of PDGF-beta receptor and ERK1/2 in cardiomyocytes was increased after short-term stimulation of PDGF-BB. Protein expression of PDGF-beta receptor and ERK1/2 was increased after long-term stimulation of PDGF-BB. [(3)H]-leucine incorporation into the cultured myocytes induced by PDGF-BB was partly blocked by mitogen-activated ERK-activating kinase (MEK) inhibitor PD98059, phospholipase C (PLC) inhibitor U73122, and protein kinase C (PKC) inhibitor staurosporin aglycone, respectively. Therefore, PDGF beta receptor, ERK1/2, PLC and PKC are involved in the signal transduction of PDGF-induced growth response of rat cardiac myocytes.