We assessed cilazapril, an angiotensin-converting enzyme (ACE) inhibitor, in the treatment of patients with chronic congestive heart failure. A single 2.5-mg dose of cilazapril was given to 20 patients with chronic congestive heart failure rated as New York Heart Association functional Class II for 15 days according to our protocol. Exercise capacity, breath-by-breath oxygen analysis, and echocardiographic variables were assessed before and after treatment. Cilazapril improved peak exercise time statistically significantly (7.36 +/- 3.48 minutes vs 9.45 +/- 4.17 minutes), but peak oxygen consumption (17.45 +/- 4.19 mL/kg per minute vs 18.65 +/- 3.70 mL/kg per minute) and peak heart rate (145.5 +/- 23.7 beats/min vs 149.9 +/- 27.1 beats/min) did not increase significantly. Anaerobic threshold time (3.31 +/- 2.38 minutes vs 4.64 +/- 2.99 minutes), anaerobic threshold oxygen consumption (11.03 +/- 2.52 mL/kg per minute vs 12.77 +/- 2.92 mL/kg per minute), and anaerobic threshold ratio (63.35 +/- 7.59% vs 68.10 +/- 7.67%) were statistically significantly increased with cilazapril treatment without a significant change in anaerobic threshold heart rate (123.3 +/- 20.4 beats/min vs 122.1 +/- 20.7 beats/min). Cilazapril treatment also decreased statistically significantly the resting heart rate (91.4 +/- 20.1 beats/min vs 85.3 +/- 17.6 beats/min) during follow-np. No patient decompensated, and diuretic and digoxin doses were not changed during the study. No adverse effects of cilazapril were observed in any patient; however, the effect of cilazapril treatment-was not detected on echocardiographic variables. me conclude that the ACE inhibitor cilazapril may be useful in the treatment of patients with chronic congestive heart failure.