Lisinopril, a new converting enzyme inhibitor, was studied hemodynamically in 55 patients. The response to 2.5-, 5- and 10-mg doses showed significant increases in cardiac index and significant reductions in pulmonary artery wedge, right atrial, pulmonary arterial and systemic arterial pressures, as well as in systemic vascular resistance. Significant changes in most parameters were present at 24 hours. A dose-response relation for most parameters was noted. Over a 3-month period, 47 patients were followed up, with improvement in functional capacity and symptomatic status. Metabolic parameters did not change over time, although 26% showed evidence of reversible renal dysfunction. Only 3 patients (6.4%) required discontinuation because of adverse effects. A subgroup of patients reassessed at 3 months demonstrated maintenance of hemodynamic effects. The present study demonstrates that (1) the hemodynamic effects of lisinopril are of relatively long duration; (2) within certain limits, a dose-response relation can be defined; and (3) the drug has an acceptable long-term tolerability profile.