Final answer:
Positive inotropic agents, such as dopamine, isoproterenol, and digitalis, increase the force of myocardial contractions by influencing calcium ion levels in the heart cells, differentiating them from negative inotropic agents like beta blockers that reduce heart function.
Step-by-step explanation:
Drugs that increase the force of myocardial contraction are known as positive inotropic agents. These agents, including synthetic drugs like dopamine and isoproterenol, mimic the effects of epinephrine and norepinephrine (NE) by promoting the influx of calcium ions into cardiac cells. A higher intracellular calcium concentration escalates the strength of heart muscle contraction. The drug digitalis is an example of a positive inotropic agent that boosts contraction force by blocking the reuptake of calcium into the sarcoplasmic reticulum, resulting in heightened intracellular calcium levels. In contrast, negative inotropic agents, such as beta blockers and calcium channel blockers, reduce myocardial contraction strength. Examples of beta blockers include propranolol, which decreases heart rate and contractility.