The human heart is a powerful, muscular organ central to the circulatory system, responsible for delivering oxygen and nutrients to tissues while removing waste. About the size of a clenched fist, it operates through a coordinated series of electrical and mechanical events that keep blood flowing efficiently throughout the body.

For Emergency Medical Responders (EMRs), a foundational understanding of cardiac anatomy and physiology is essential. The heart has four chambers (two atria and two ventricles), four valves that ensure one-way blood flow, and a conduction system that generates and coordinates each heartbeat. These components work together in two circulatory loops—pulmonary and systemic—to maintain oxygenation and perfusion.

Recognizing early signs of cardiac distress, using tools like ECGs, and performing interventions such as CPR or AED use all depend on a clear understanding of how the heart functions. From arrhythmias to cardiac arrest, EMRs are often the first line of defense in identifying and managing life-threatening cardiac conditions.