Hemodynamic effects of oral hydralazine (200 to 400 mg/d) were evaluated in 11 patients with chronic heart failure after short-term (24 hours) and long-term (average, 8.3 months) therapy. In seven of 11 patients, hemodynamic changes were evaluated after withdrawal of hydralazine. During early study, cardiac index, stroke volume index, and stroke work index increased by an average of 56%, 59%, and 68%, respectively, and systemic vascular resistance decreased by 39%. During late study, cardiac index (+65%), stroke volume index (+88%), and stroke work index (+ 98%) remained higher and systemic vascular resistance (-41%) lower than control values. Withdrawal of hydralazine caused a decrease in cardiac index, stroke volume index, and stroke work index and an increase in systemic vascular resistance. Heart rate and arterial, pulmonary capillary wedge, and right atrial pressures did not change significantly. These findings suggest that oral hydralazine produces sustained beneficial hemodynamic effects in patients with chronic heart failure.