A large number of naturally occurring and synthetically prepared chemical agents produce a positive inotropic effect on the heart. Analogues of these compounds have been isolated, prepared, and tested, and a number of them also have positive inotropic effects (see Tables 1-6). A number of reviews on inotropic agents and their possible mechanisms have been published (1-7). Because of space limitations, only compounds that have had extensive pharmacological investigation will be discussed here . Thus, we will consider newer adrenergic agents , new phosphodiesterase inhibitors , some polypeptides, and a number of miscellaneous compounds that have interesting pharmacological properties. The choice of compounds to be discussed was based on the interests of the authors; our readers may disagree with these choices.