Although the short-term hemodynamic and clinical responses to angiotensin-converting enzyme inhibition in patients with congestive heart failure (CHF) are well known, little information is available about the long-term results of captopril therapy. In the present study, 15 stable outpatients received captopril therapy and were followed for a mean of 19 months (range 6 to 27) with serial clinical assessments and measurements of exercise tolerance, ejection fraction (EF) and cardiothoracic ratio. Exercise tolerance on a modified Naughton protocol improved from 10.5 +/- 2.7 to 12.7 +/- 2.4 minutes (mean +/- standard deviation) at 3 months (p less than 0.001), tended to increase progressively up to 12 months and remained significantly increased even after 24 months (9.7 +/- 1.8 vs 13.5 +/- 4.0 minutes, p less than 0.05). However, individual responses were variable; 4 patients did not show measurable improvement. Left ventricular EF increased from 0.20 +/- 0.06 to 0.25 +/- 0.06 (p less than 0.01) at 3 months and remained higher (0.30 +/- 0.12, p less than 0.02) at latest follow-up. Cardiothoracic ratio decreased from 0.59 +/- 0.04 to 0.56 +/- 0.05 (p less than 0.02) at 3 months and remained significantly lower at 12 months and at latest follow-up, although again individual responses were variable. Clinical responses generally correlated with these objective measurements, with clinical classification on a scale modified from the New York Heart Association classification improving from 3.0 +/- 0.6 to 2.3 +/- 0.5 (p less than 0.01) at 3 months and remaining improved throughout the follow-up period.(ABSTRACT TRUNCATED AT 250 WORDS)