Which drug causes vasodilation and affects cyclic AMP levels?

Milrinone is the correct choice as it is a phosphodiesterase inhibitor that leads to increased levels of cyclic AMP within cardiac and vascular tissue. This elevation in cyclic AMP causes smooth muscle relaxation, resulting in vasodilation. Milrinone specifically enhances myocardial contractility and promotes vasodilation by preventing the breakdown of cyclic AMP, which is a critical second messenger in various physiological processes.

In contrast, dopamine primarily acts on dopamine receptors and can have various effects, including increasing heart rate and myocardial contractility, but it does not focus specifically on cyclic AMP to induce vasodilation. Isoproterenol is a non-selective beta-adrenergic agonist that can cause vasodilation but does not primarily act through a cyclic AMP mechanism involving phosphodiesterase inhibition. Ephedrine is a mixed-action sympathomimetic that primarily works through adrenergic receptor stimulation rather than directly affecting cyclic AMP levels or inducing vasodilation through that pathway.