The mechanism of action of these drugs is inhibition of phosphodiesterase in the heart and vascular wall with accumulation of cAMP. These 'inodilators' increase myocardial contractility without a major rise in heart rate or myocardial oxygen demands, and produce a fall in peripheral vascular resistance without a major blood pressure lowering effect. They increase cardiac compliance and have a prolonged duration of action. They can be used judiciously, mainly as an adjunct to standard therapy in patients in whom cardiac output is (relatively) low, for instance during postmyocardial infarction shock and after cardiopulmonary bypass surgery. Severe hypotension does not usually occur but can be a major limitation in some patients.
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