The effect of endothelin (ET) on rat cardiac myocytes cultured in a serum‐free, defined medium was determined. ET stimulated cardiac myocyte hypertrophy in a dose‐dependent manner as determined by the protein synthesis and cell surface area. Since the myocyte hypertrophy was abolished by H‐7, a protein kinase C inhibitor, ET‐receptor mediated protein kinase C activation may be involved in cardiac myocyte hypertrophy. At the same time, ET also stimulated myocyte contractility in this medium, and this stimulatory effect was inhibited by nicardipine. This result indicates that the influx of extracellular calcium ion is necessary for the stimulation of contractility induced by ET.