inotropy

Inotropy is the word for the heart muscle's contractile strength — how forcefully it can squeeze. To increase inotropy is to make each beat punchier; the term comes from Greek roots meaning fiber and turning, the idea of how vigorously the muscle fibers act.

Inotropy and contractility describe the same property. An influence that increases the force of contraction is called positive inotropic; one that weakens it is negative inotropic. Adrenaline, sympathetic nerve activity, and drugs such as digoxin are positive inotropes; certain beta-blockers and calcium channel blockers are negative inotropes.

At the cellular level, positive inotropy usually works by increasing the calcium available to the contractile proteins inside heart muscle cells, so each contraction develops more tension. The result, at the chamber level, is more complete emptying and a larger stroke volume at the same filling.

Manipulating inotropy is central to treating shock and severe heart failure, but it is a double-edged tool: driving a struggling heart harder raises its oxygen demand and can be harmful if overused, so positive inotropes are generally reserved for short-term rescue.