Amrinone and milrinone are bipyridine derivatives that are relatively selective inhibitors of cGMP-inhbited, cyclic AMP phosphodiesterase (type III).

These agents cause vasodilation (decreased afterload) and increase myocardial contractility.

Milrinone is the agent of choice among the phosphodiesterase inhibitors for short-term parenteral support in severe heart failure patients. Oral formulations are not used due to intolerable side-effects including increases in mortality.