The document discusses the anatomy and basic function of the human heart. It describes the three main tissues that make up the heart - the outermost pericardium and epicardium, middle myocardium, and innermost endocardium. It then explains the four chambers of the heart - the two upper atria that receive blood and two lower ventricles that pump blood out. The document outlines the pulmonary and systemic circulations, describing the pathways that oxygenated and deoxygenated blood follow. It also reviews the locations and roles of the heart's five valves in regulating blood flow during heart relaxation and contraction.