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How does the heart act as a muscular pump?

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Silhouette diagram of the human body highlighting the heart and major blood vessels, with labeled arteries in red and veins in blue to show the structure of the cardiovascular system. — Circulatory system Human circulatory system.

The heart functions as a muscular pump primarily through the action of the myocardium, the middle layer of the heart wall composed of specialized cardiac muscle cells. Its pumping ability relies on two key characteristics: contractility and rhythmicity.12

Mechanism of Contraction

The myocardium contains branching muscle fibers organized into layers that wrap around the heart chambers. These fibers produce a wringing movement that efficiently squeezes blood out of the heart with each beat. At the cellular level, this is driven by sarcomeres—contractile units containing actin and myosin filaments. When these proteins interact, the muscle fibers shorten, decreasing the size of the heart chambers and ejecting blood into the circulatory system.31

Coordination and Energy

This process is highly coordinated:
* Communication: Intercalated discs link cardiac cells, allowing for the rapid electrical communication necessary for synchronized contraction.3
* Regulation: The sinoatrial node acts as a pacemaker, regulating the rhythm of contractions.1
* Energy: Mitochondria occupy a significant portion of cardiac cells, providing the energy required for continuous, rhythmic pumping.3