A PDE3 inhibitor and ERG1 channel blocker (IC50s = 10.7, 13.2, and 1.1 μM for PDE3A, PDE3B, and ERG1, respectively); increases contractile tension in isolated ventricular muscles of dog, cat, rabbit, and guinea pig in a dose-dependent manner; increases right ventricular pressure with no effect on heart rate in dog models of tricuspid insufficiency- and pulmonary stenosis-induced congestive heart failure; increases contractility and coronary flow while decreasing heart rate in a guinea pig model of aortic stenosis-induced congestive heart failure