Pharmacological therapy in cases of chronic congestive heart failure (CHF) is usually evaluated by maximal exercise time. To assess the effect of an angiotensin converting enzyme inhibitor, ramipril, 223 patients with moderate CHF were studied in 24 centres in four Nordic countries in a randomized, double-blind, placebo-controlled, parallel group design. The study drug was titrated from 1.25 mg to a maximum of 10 mg once daily (o.d) over a period of 4 weeks (mean dose 8 mg). A symptom-limited bicycle exercise test, starting at 30 watts and increasing by 10 watts.min-1, was used to evaluate exercise capacity. Reproducible tests were required at baseline, and the test was repeated after 4, 8 and 12 weeks of treatment. Seven deaths were recorded in the placebo group and one death in the ramipril group. A total of 195 patients completed 12 weeks of treatment (placebo group n = 91, ramipril group n = 104). The groups had similar baseline characteristics. Maximal exercise time was increased by mean (SD) 35 s (9) and 41 s (8) in the placebo and ramipril groups, respectively. The adjusted difference between the groups at 12 weeks was 9 s (12) (ns). A significant decrease in blood pressure and rate-pressure product at rest and at end of exercise was obtained by ramipril as compared with placebo. Significantly fewer patients deteriorated in NYHA class from baseline to 12 weeks of ramipril treatment compared to placebo (P = 0.012). Concomitant medication for CHF increased significantly in the placebo group as compared with ramipril-treated patients (P = 0.003).(ABSTRACT TRUNCATED AT 250 WORDS)