OPC-8212, a newly synthesized noncatecholamine, nonglycosidic, orally effective inotropic agent, has been shown to exert a potent cardiotonic action in acute administration to patients with heart failure. However, its long-term effect has not yet been established. Eight patients with dilated cardiomyopathy (New York Heart Association functional class II-III) were given a single dose of 60 mg of OPC-8212 daily for 4 to 8 weeks. OPC-8212 produced symptomatic improvement in four patients. Though there were no detectable changes in arterial pressure and left ventricular end-diastolic dimension, heart rate and end-systolic dimension significantly decreased after administration of OPC-8212. Baseline fractional shortening rose significantly and depression of shortening in response to acute pressor stress (afterload mismatch) was corrected after OPC-8212. The end-systolic pressure-dimension relation was shifted to the left with a steeper slope. These findings indicate that the inotropic state was substantially enhanced by the drug. No adverse effects were observed in any patient. Thus, the drug appears to hold promise for the chronic treatment of patients with moderate congestive heart failure who are essentially asymptomatic at rest, but develop severe impairment of cardiac function in a stressed state.