Contractility is a concept of the strength of the myocardium. Think of contractility as a reflection of the heart. There are no direct clinical measurements of contractility, but it is influenced by various factors. Inotropic drugs are drugs that increase the force of contraction (they have positive contractility effects). Some examples of positive inotropic drugs include digoxin, sympathomimetic agents (like epinephrine, dopamine, and dobutamine), and milrinone. Stimulation of the sympathetic nervous system—like in the fight/flight response or the adrenaline rush—increases contractility.
Inhibitory influences on contractility might involve drugs or pathophysiologies. Drugs that inhibit contractility (reduce the force of contraction) are referred to as negatively inotropic. Some negative inotropic drug categories include calcium channel blocking agents, beta-adrenergic blocking agents, and many other antidysrhythmic drugs. Pathological inhibitions of contractility may be hypoxia of the myocardium, hypercapnia, and metabolic acidosis.