The cardiotonic effect of AR-L 115 BS was assessed in 5 dog heart-lung preparations in which cardiac function had been severely depressed by pentobarbital. AR-L 115 BS in doses of 1-60mg improved cardiac function in a dose-dependent manner and at 30 and 60mg improved it beyond control values. These doses of AR-L 115 BS, however, produced neither a significant increase in heart rate nor arrhythmias. The results indicate that the drug would be of use in the treatment of heart failure.