An inhibitor of PDE3 (IC50s = 0.45 and 1 μM for PDE3A and PDE3B, respectively); selective for PDE3 over PDE1, PDE2, PDE4, PDE5, and PDE7 (IC50s = 263, >300, 17.5, 49.1, and 58.3 μM, respectively); increases contractile force in anesthetized dogs at 0.1-1 mg/kg; increases contractile force in models of propranolol- and verapamil-induced heart failure in anesthetized dogs at 30 μg/kg followed by a 3 μg/kg infusion; decreases mean aortic pressure and increases venous compliance in anesthetized dogs at 10 μg/kg followed by a 1.7-2.4 μg/kg per minute infusion