To assess acute hemodynamic effects and exercise capacity of an intravenously administered single dose of captopril and to compare the acute response with chronic variation in hemodynamic and functional parameters after long-term oral administration, (in order to determine the profile of responders and non-responders) we studied 12 patients with chronic congestive heart failure due to primary dilated cardiomyopathy (11 pts) and ischemic heart disease (1 pt). Hemodynamic response was assessed using transthoracic electric impedance with cardiac output measurement. The exercise capacity was determined using multistage bicycle ergometer symptoms limited stress test. The hemodynamic and functional evaluation--resting cardiac output, exercise capacity (Ex. Dur.) and cardiac output rise at maximum workload (% CO)--were investigated at first as a control; after i.v. captopril administered in 10 min (25 mg) (acute); after captopril per os (25-75 mg for 30 days) (chronic) and after 5 days of withdrawal (wash out). (Table: see text). Improvement of left ventricular performance mainly during exercise after acute and chronic administration of captopril occurred, as evidenced from cardiac output increase at maximum work load, and rise of exercise duration. Moreover, our data suggest that captopril may have a sustained beneficial effect, for a few days, even after drug withdrawal. Nevertheless, the lack of correlation in single cases between acute and chronic response, also indicates that captopril deserves further study to determine its role in acute and/or chronic management of congestive heart failure in order to choose the ideal strategy.