Cyclic adenosine monophosphate effects on the myocardium: a man who blows hot and cold with one breath

Agents that increase cellular cyclic adenosine monophosphate (cyclic AMP) levels exert several effects on cardiac function. These include increases in heart rate and both the force of contraction and rate of relaxation. The latter effects, which might appear to be contradictory, actually represent essential components of the response needed to allow the heart to increase its stroke volume when heart rate is accelerated. This article reviews the mechanisms by which cyclic AMP exerts both contraction-promoting and relaxation-promoting effects in the integrated response of the heart to sympathetic stimulation.