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 (< 70 years vs. greater-than-or-equal-to 70 years), duration of heart failure (< 1 year vs. > 1 year), presence of digoxin treatment, or the dosing schedule employed. This large study showed that use of captopril in mild to moderate heart failure in the primary care setting has a favorable risk-benefit profile and is associated with meaningful improvements in clinical status and functional capacity.