Which agents or changes have a negative inotropic effect on the heart?

Acetylcholine (ach)-a negative inotropic effect is one that decreases myocardial contractility. contractility is the ability to develop tension at a fixed muscle length. factors that decrease contractility are those that decrease the intracellular [ca 2-1. increasing heart rate increases intracellular [ca2+] because more ca2� ions enter the cell during the plateau of each action potential. sympathetic stimulation and norepinephrine increase intracellular [ca2+] by increasing entry during the plateau and increasing the storage of ca 2+ by the sarcoplasmic reticulum (sr) [for later release]. cardiac glycosides increase intracellular [ca 2�] by inhibiting the na+k+ pump, thereby inhibiting na+ca21- exchange (a mechanism that pumps ca2+ out of the cell). acetylcholine (ach) has a negative inotropic effect on the atria.