Enoximone is a phosphodiesterase 3 (PDE3) inhibitor (IC50 = 5.9 µM).¹ It is selective for PDE3 over PDE1, -2, and -4 (IC50s = 2,100, 2,900, and 21.1 µM, respectively). Enoximone increases the force of contraction and cAMP levels in isolated canine right ventricular trabeculae, an effect that can be reversed by carbamoylcholine (carbachol).² In vivo, enoximone (0.1-1 mg/kg) increases cardiac contractile force in dogs.³ Formulations containing enoximone have been used in the treatment of congestive heart failure.