Angiotensin-converting enzyme inhibitors (ACEI) are often used in preventing and treating heart failure due to regurgitant valve disease. The majority of patients with symptomatic rheumatic heart disease (RHD) have significant mitral stenosis (MS) and are denied ACEI therapy, because of the fear of hypotension in the presence of fixed obstruction. The authors assessed the safety and efficacy of ACEI in 109 consecutive patients with RHD and with significant mitral stenosis (mitral valve orifice, MVO < 1.5 cm2)and with NYHA class III or IV heart failure symptoms. Mean age was 33.1+/-12 years, systolic blood pressure (BP) was 111+/-10, and diastolic BP was 73+/-8 mm Hg. MS was significant in 100 patients with mitral regurgitation in 46, aortic regurgitation in 19, and pulmonary hypertension in 60 patients. After initial stabilization, enalapril 2.5 mg bid was started in hospital and titrated up to 10 mg bid over 2 weeks. NYHA status, Borg score, and 6-minute walk test were assessed at baseline, and at 1, 2, and 4 weeks. Seventy-nine of the 100 patients who completed the study had severe MS (MVO < 1.0 cm2). Enalapril was well tolerated by all study patients without hypotension or worsening of symptoms. NYHA class (3.2+/-0.5 baseline vs 2.3+/-0.5 at 4 weeks, p < 0.01) Borg Dyspnea Index (7.6+/-1.3 vs 5.6+/-1.3, p < 0.01), and 6-minute walk distance (226+/-106 vs 299+/-127 m, p < 0.01) improved significantly with enalapril. Patients with associated regurgitant lesions showed more improvement in exercise capacity (120+/-93 vs 39+/-56 m, p < 0.001). Enalapril was well tolerated in patients with RHD with moderate and severe MS. Irrespective of the valve pathology, enalapril improved functional status and exercise capacity with maximum benefit in patients with concomitant regurgitant valvular heart disease.