Effect of vasodilator drugs on exercise performance in cardiac failure. Comparison of hydralazine and prazosin.

Although vasodilator drugs cause haemodynamic improvement at rest, their effect on the overall exercise response is uncertain. Nine patients with severe diuretic dependent cardiac failure were studied before and during upright bicycle exercise, after the double blind administration of equi- hypotensive doses of hydralazine (H) 75 mg, prazosin (Pr) 3 mg, and placebo (P1). The ventilatory response and oxygen uptake were monitored continuously. Cardiac output was measured during the third mtnute of steady state exercise by the CO2 rebreathing method.