The human heart is a muscular organ that provides a continuous blood circulation through the cardiac cycle and is one of the most vital organs in the human body.[1] The heart is divided into four main chambers: the two upper chambers are called the left and right atria and two lower chambers are called the right and left ventricles.There is a thick wall of muscle separating the right side and the left side of the heart called the septum. Normally with each beat the right ventricle pumps the same amount of blood into the lungs that the left ventricle pumps out into the body. Physicians commonly refer to the right atrium and right ventricle together as the right heart and to the left atrium and ventricle as the left heart.[2]

The electric energy that stimulates the heart occurs in the sinoatrial node, which produces a definite potential and then discharges, sending an impulse across the atria. In the atria the electrical signal move from cell to cell [3] while in the ventricles the signal is carried by specialized tissue called the Purkinje fibers [4]which then transmit the electric charge to the myocardium

The human heart and its disorders (cardiopathies) are studied primarily by cardiology.

The human heart has a mass of between 250 and 350 grams and is about the size of a fist.[5]

It is enclosed in a double-walled protective sac called the pericardium.[6] The superficial part of this sac is called the fibrous pericardium. This sac protects the heart, anchors its surrounding structures, and prevents overfilling of the heart with blood.

The outer wall of the human heart is composed of three layers. The outer layer is called the epicardium, or visceral pericardium since it is also the inner wall of the pericardium. The middle layer is called the myocardium and is composed of muscle which contracts. The inner layer is called the endocardium and is in contact with the blood that the heart pumps. Also, it merges with the inner lining (endothelium) of blood vessels and covers heart valves.[7]

The human heart has four chambers, two superior atria and two inferior ventricles. The atria are the receiving chambers and the ventricles are the discharging chambers.

The pathways of blood through the human heart is part of the pulmonary and systemic circuits. These pathways include the tricuspid valve, the mitral valve, the aortic valve, and the pulmonary valve.[8] The mitral and tricuspid valves are classified as the atrioventricular (AV) valves. This is because they are found between the atria and ventricles. The aortic and pulmonary semi-lunar valves separate the left and right ventricle from the pulmonary artery and the aorta respectively. These valves are attached to the chordae tendinae (literally the heartstrings), which anchors the valves to the papilla muscles of the heart.

The interatrioventricular septum separates the left atrium and ventricle from the right atrium and ventricle, dividing the heart into two functionally separate and anatomically distinct units.