This study aimed to determine the efficacy and dose requirements of captopril in reducing functional mitral regurgitation (MR) in patients with dilated heart failure. A randomized, double-blind, placebo-controlled trial was conducted on 28 ambulatory patients with New York Heart Association (NYHA) class II or III heart failure and controlled ischaemic dilated heart failure. Patients were given incremental daily doses of 25 mg, 50 mg, and 100 mg of captopril for four weeks, followed by a two-week placebo washout. The results showed that significant improvements in MR were observed only in the captopril group, with a threshold dose of 50 mg/day and a further decrease at 100 mg/day. Other improvements, such as increased stroke volume, decreased systemic vascular resistance, reduced left atrial area, and increased deceleration time, were noted only at the 100 mg/day dose. No significant changes were observed in heart rate, mean arterial blood pressure, serum creatinine, or serum potassium. The study concluded that captopril is effective in reducing functional MR in dilated heart failure, but high doses (50-100 mg/day) are necessary to achieve significant additive effects over conventional treatment.This study aimed to determine the efficacy and dose requirements of captopril in reducing functional mitral regurgitation (MR) in patients with dilated heart failure. A randomized, double-blind, placebo-controlled trial was conducted on 28 ambulatory patients with New York Heart Association (NYHA) class II or III heart failure and controlled ischaemic dilated heart failure. Patients were given incremental daily doses of 25 mg, 50 mg, and 100 mg of captopril for four weeks, followed by a two-week placebo washout. The results showed that significant improvements in MR were observed only in the captopril group, with a threshold dose of 50 mg/day and a further decrease at 100 mg/day. Other improvements, such as increased stroke volume, decreased systemic vascular resistance, reduced left atrial area, and increased deceleration time, were noted only at the 100 mg/day dose. No significant changes were observed in heart rate, mean arterial blood pressure, serum creatinine, or serum potassium. The study concluded that captopril is effective in reducing functional MR in dilated heart failure, but high doses (50-100 mg/day) are necessary to achieve significant additive effects over conventional treatment.