An inhibitor of PDE2 and PDE3; inhibits cAMP hydrolysis (IC50 = 4.1 μM in rabbit heart ventricles) selectively over cGMP hydrolysis (IC50 = 171 μM); induces positive inotropic (EC50 = 100 μM) and negative chronotropic effects in isolated rabbit papillary muscle and right atria, respectively; a substrate for AOX1