Objective: To evaluate the effects of the angiotensin converting enzyme inhibitor perindopril on six minute walking distance and quality of life in very old patients with left ventricular systolic dysfunction. Design: Prospective, double blind placebo controlled trial. Setting: Medicine for the elderly day hospital. Patients: 66 patients (average age 81) with left ventricular systolic dysfunction identified by echocardiography. Interventions: 10 weeks of treatment with titrated doses of perindopril or placebo. Main outcome measures: Six minute walking distance 10 weeks following treatment, quality of life measurements including the Minnesota living with heart failure questionnaire and the 36 item short form health survey. Results: In patients with left ventricular systolic dysfunction, six minute walking distance was significantly increased in the treatment group (37.1 m) compared with the placebo group (-0.3 m, p < 0.001). The medication was well tolerated and there were no significant adverse events. Conclusions: Six minute walking distance is improved considerably by treatment with perindopril in older patients with heart failure caused by left ventricular systolic dysfunction.