The study was designed to evaluate the prognostic value of the 6-minute walk test in stable outpatients with heart failure. We prospectively studied 43 patients (6 women and 37 men) who had chronic heart failure secondary to ischemic heart disease or idiopathic cardiomyopathy. All patients had left ventricular systolic dysfunction (ejection fraction, < or = 0.40), and they were in stable New York Heart Association functional class II or III heart failure. All patients were evaluated by M-mode and 2-dimensional echocardiography. At the outset, walking distances of all the patients were evaluated by the 6-minute walk test. The patients were divided into 2 groups: Group I, patients with a 6-minute walk test distance of < or = 300 m; and Group II, patients with a 6-minute walk test distance of > 300 m. The patients were then monitored for a period of 2 years in regard to cardiac death. The mortality rate was significantly higher in patients with a 6-minute walk test distance of < or = 300 m than in patients with a 6-minute walk test distance of > 300 m (79% vs 7%; P <0.001). The death risk was found to be significantly higher in patients with a distance of < or = 300 m (P=0.005). The death risk was also higher in patients whose left ventricular ejection fraction was < or = 0.30 (P=0.02). We conclude that a 6-minute walk test distance of < or = 300 m is a simple and useful prognostic marker of subsequent cardiac death in patients with mild-to-moderate heart failure.