The effect of taurine on angiotensin II-induced hypertrophy of cultured neonatal rat heart cells (myocytes and nonmyocytes) was examined. Angiotensin II (1-100 nM) alone caused an increase in the rate of protein synthesis and the surface area of myocytes without altering the rate of DNA synthesis or cell number. It also mediated an increase in DNA synthesis and in cell number of nonmyocytes. Exposure of the cells to taurine (20 mM) in the absence of angiotensin II had no effect on either hyperplastic growth or hypertrophy of the two types of cultured cardiac cells. However, myocytes pretreated with 20 mM taurine exhibited reduced responsiveness to angiotensin II. Following a 24 hr pretreatment with 20 mM taurine, the stimulation in protein synthesis by angiotensin II (1 nM) was significantly suppressed. Similarly, taurine treatment of nonmyocytes reduced the degree of angiotensin II-induced promotion of hyperplastic growth (DNA synthesis and cell number). Finally, taurine partially prevented the rise in [Ca2+]i mediated by angiotensin II in cardiac cells. The present results indicate that taurine is an effective inhibitor of angiotensin II action. The possibility that the beneficial effects of taurine in the treatment of heart failure might be related to its suppression of angiotensin II-mediated cellular responses is discussed.