The human heart is a vital muscular organ responsible for pumping blood throughout the body, ensuring the delivery of oxygen and nutrients to tissues and the removal of carbon dioxide and waste products. It is located in the thoracic cavity between the lungs and consists of four chambers: two upper atria and two lower ventricles. Blood flow through the heart is regulated by four main valves: the tricuspid, pulmonary, mitral, and aortic valves. The heart operates through two primary circulation pathways: pulmonary circulation, which transports deoxygenated blood to the lungs and returns oxygenated blood to the heart, and systemic circulation, which distributes oxygenated blood to the body and returns deoxygenated blood to the heart.

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The cardiac cycle comprises two phases: diastole, where the heart muscles relax and chambers fill with blood, and systole, where the heart muscles contract, pumping blood out of the chambers. The heart's rhythmic pumping is controlled by its electrical conduction system, starting with the sinoatrial (SA) node, the natural pacemaker, followed by the atrioventricular (AV) node, the bundle of His, and the Purkinje fibers. These structures ensure coordinated contraction of the heart chambers.

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The heart itself requires a constant supply of oxygenated blood, which is delivered by the coronary arteries. The left coronary artery branches into the left anterior descending artery and the circumflex artery, while the right coronary artery supplies the right side of the heart and part of the left ventricle. The autonomic nervous system regulates heart function, with the sympathetic nervous system increasing heart rate and contraction force during stress or activity, and the parasympathetic nervous system decreasing them during rest.

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Various conditions can affect heart function, including coronary artery disease, which reduces blood flow to the heart muscle, heart failure, where the heart cannot pump blood efficiently, arrhythmias, which are abnormal heart rhythms, and valvular heart disease, which involves dysfunction of the heart valves. Understanding the intricate workings of the heart underscores the importance of cardiovascular health and the impact of diseases on overall well-being.