What is a key characteristic of milrinone's mechanism of action?

Milrinone is a phosphodiesterase inhibitor that primarily acts by increasing the levels of cyclic AMP (cAMP) within cardiac and vascular smooth muscle cells. This increase in cAMP leads to enhanced myocardial contractility (positive inotropic effect) and induces vasodilation, which helps to reduce pulmonary and systemic vascular resistance. The increased cAMP levels allow for better calcium handling in the heart muscle cells, thus improving cardiac output, especially in patients with heart failure.

The action of milrinone as a phosphodiesterase inhibitor illustrates its role in both improving heart function and reducing the workload on the heart, making it particularly useful in situations where cardiac output is compromised.