The anatomy of the heart includes the organ itself, which is made up of four chambers, multiple valves separating the chambers, and a thick wall of cardiac muscle throughout, one of three layers of heart wall. It also may include the major vessels immediately entering and exiting the heart, such as the aorta, pulmonary arteries and veins, and vena cava, as well as the nerves penetrating the heart and powering the contractions. The anatomy of the heart makes possible a closed circuit of blood flow in which deoxygenated blood is pumped from the heart to the lungs to pick up oxygen, then back through the heart and out to the body via the aorta to distribute this oxygen-rich blood to the body’s tissues. Cycled back to the heart by the veins once the oxygen has been removed, the blood is then circulated back through the lungs as the circuit begins again.
Roughly the size of two stacked fists, the human heart is found within in the ribcage, located behind the sternum or breastbone in the center of the chest. The lowermost portion curves slightly to the left and forms a soft point. This organ can be divided into right and left sides, with two chambers on each side: an atrium and a ventricle. As the uppermost chambers, the right and left atria are where blood is returned to the heart, with deoxygenated blood from the body carried to the right atrium and newly oxygenated blood from the lungs brought to the left atrium.
In the anatomy of the heart, each half of the organ acts as a separate pumping system. The systemic circuit involves the left half, in which oxygenated blood cycled back from the lungs by the pulmonary veins enters the left side of the heart, dumped into the left atrium. It then passes through a valve at the bottom of the atrium called the mitral valve, entering the left ventricle below before being pumped out of the heart by way of the aortic semilunar valve into the aorta, the major blood vessel exiting the top of the heart. From there it is distributed throughout the body.
Meanwhile, on the right side of the heart, the pulmonary circuit begins. Here, deoxygenated blood returned from the body by the superior and inferior vena cava, the large veins approaching the organ from above and below, enters the right atrium. Passing through the tricuspid valve en route to the right ventricle, it is subsequently pumped out of the heart through the pulmonary semilunar valve before entering the pulmonary arteries, which carry it to the lungs for re-oxygenation. Once this is completed, the pulmonary veins bring the blood back to the left side of the heart, completing the loop facilitated by the four-chambered anatomy of the heart.
These four chambers are enclosed by three layers of tissue that make up the anatomy of the heart wall: the epicardium, myocardium, and endocardium. The epicardium is the outermost layer of the heart wall and is contiguous with the innermost layer of the pericardium, the fibrous sac enveloping and protecting the heart. Inside of the epicardium is the myocardium, the layer of cardiac muscle that contracts to produce the pumping motion that pushes blood through the heart’s chambers. The innermost layer of the heart wall is the endocardium, against which the blood moves on its path through the organ’s interior.