Lixazinone selectively inhibits the high-affinity form of cyclic AMP phosphodiesterase (type IV) isolated from human platelets with only weak effects on both the nonspecific and cyclic GMP-sensitive phosphodiesterases. The inhibitor reduces both maximum velocity and substrate affinity of the type IV enzyme. Lixazinone exhibits marked selectively for the platelet high-affinity enzyme. It also has significant inhibitory effects on cardiac membrane-bound phosphodiesterase. Lixazinone may be useful as an agent to increase cardiac output in the treatment of congestive heart failure. It is a potent PDE3 inhibitor. Lixazinone suppresses folic acid-induced proliferation of rat tubular epithelial cells in vivo.