A large-scale, prospective, 8-week, office-based study was conducted to evaluate the effects of adding captopril to a therapeutic regimen of diuretic and digoxin or diuretic alone in the management of patients with mild to moderate congestive heart failure (CHF). A total of 2218 primary care physicians evaluated 6669 patients over the study period for efficacy parameters, which included changes in a modified New York Heart Association (NYHA) functional classification, symptomatology, and daily activity levels. Overall, 63.8% of evaluated patients improved with regard to functional ability, with 19% improving two or more modified NYHA classes. Symptoms of CHF, including dyspnea on exertion, fatigue, and orthopnea and signs, including rales and peripheral edema, were reduced in 86% of these patients: 41.5% demonstrated mild improvement; 30.0%, moderate improvement; and 14.5%, marked improvement. Three parameters, with which patients reported having difficulty at study entry, were assessed serially to evaluate changes in functional capacity; 78.5% of patients reported an increased walking distance, 72.3% had increased capacity for climbing stairs, and 60.2% had improved capacity for individual recreational activities. Adverse experiences were reported in 18.1% of all patients; 4.9% of patients withdrew from the study because of an adverse effect. Combination therapy with captopril and diuretic for CHF was shown to be safe and effective regardless of patient age (less than 70 years vs. greater than or equal to 70 years), duration of heart failure (less than 1 year vs. greater than 1 year), presence of digoxin treatment, or the dosing schedule employed.(ABSTRACT TRUNCATED AT 250 WORDS)