Objective: Rho-dependent kinases serve as downstream effectors of several vasoconstrictor systems, whose activities are upregulated in congestive heart failure. The present study evaluated the renal and cardiac effects of Y-27632, a highly selective Rho-kinase inhibitor, in an experimental model of volume-overload congestive heart failure. Methods: The effects of acute administration of Y-27632 (0.3 mg/kg) on renal hemodynamic and clearance parameters, and of chronic treatment (10.0 mg/kg/day for 7 days, via osmotic minipumps) on cardiac hypertrophy and cumulative sodium excretion, were studied in male Wistar rats with aorto-caval fistula and control rats. Results: Injection of Y-27632 decreased renal vascular resistance (from 40.4±4.6 to 26.0±3.1 resistance units, p<0.01) in heart failure rats, associated with a significant increase in total renal blood flow (+34%), and in cortical and medullary blood flow (by 37% and 27%, respectively). These values were significantly higher than those observed in control rats, and occurred in spite of a decrease in mean arterial pressure (of -15 mm Hg). Despite the marked renal vasodilatory effect, the drug did not alter glomerular filtration rate and sodium excretion by the kidney. Similarly, chronic administration of Y-27632 did not alter daily or cumulative renal sodium excretion in rats with heart failure, but was associated with a significant decrease in heart/body weight ratio, an index of cardiac hypertrophy (Control: 0.32± 0.007%, heart failure: 0.46±0.017%, heart failure + Y-27632: 0.37±0.006%). Conclusions: The findings suggest that Rho-kinase dependent pathways are involved in the mechanisms of renal vasoconstriction and cardiac hypertrophy in rats with volume-overload heart failure. Selective blockade of these signaling pathways may be considered as an additional tool to improve renal perfusion and attenuate cardiac hypertrophy in heart failure.