To evaluate the safety and efficacy of the inotropic agent OPC-8212 in patients with chronic congestive heart failure, 76 patients with impaired cardiac function and diminished exercise tolerance were studied. They were randomized to 12 weeks of double-blind therapy with either 60 mg/day of OPC-8212 or placebo. The study drug was added to their baseline medical regimen. The primary study outcome was the combined outcome of the time to either mortality (of all cause) or substantial worsening of heart failure (major morbidity), whichever occurred first. Treatment with OPC-8212 significantly (p less than 0.01) decreased the combination of major morbidity/mortality over 12 weeks of therapy. Quality of life, assessed by the Sickness Impact Profile questionnaire, was significantly improved in patients receiving OPC-8212 (p less than 0.01). Furthermore, ventricular premature contractions as assessed by 24-hour Holter monitoring were not increased with OPC-8212 treatment. Although patients treated with OPC-8212 were able to reach a significantly higher peak oxygen uptake and exercise longer during symptom-limited exercise, when data were analyzed as percent change from baseline, the absolute increases were small. These results suggest that OPC-8212 is beneficial in treating patients with congestive heart failure and that further evaluation of this new inotropic agent is warranted.