Heart

The heart is a muscular organ composed primarily of specialized myocardial cells, functioning as the central pump of the circulatory system. In vertebrates, the heart is anatomically divided into four chambers: two atria and two ventricles. Its primary role is to rhythmically contract and relax, thereby propelling blood through the pulmonary and systemic circulations to supply oxygen and nutrients to tissues and remove metabolic waste products.

The heart's structure is characterized by multilayered myocardium, connective tissue, valves, coronary vessels, and a conduction system that coordinates its electrical and mechanical activity.

Evolutionarily, the vertebrate heart has developed from a simple contractile tube in early chordates to a complex, chambered organ capable of supporting high metabolic demands in mammals and birds.