Anatomy of the HeartThe heart is divided into four compartments called chambers. There are two upper chambers called the atria (singular atrium) and two lower chambers called the ventricles. The atrial septum divides the right and left atria. The ventricular septum divides the right and left ventricles. Blood from the body is carried into the heart’s right atrium by blood vessels called the vena cava. The inferior vena cava brings blood from the legs and the lower part of the body, while the superior vena cava brings blood from the head, neck, and arms. When the right atrium fills with blood, it contracts, sending blood to the right ventricle. When the right ventricle fills with blood, it contracts, sending blood to the lungs through blood vessels called the pulmonary arteries. In the lungs, blood picks up oxygen, and then returns to the heart’s left atrium through blood vessels called the pulmonary veins. When the left atrium contracts, it sends blood to the left ventricle, from the left ventricle, blood is pumped out the aorta and through the body.
Heart valves act as one-way doors, making sure that blood flows in the correct direction through the heart. Four valves control the blood flow in the heart: 1) The tricuspid valve regulates blood flow from the right atrium into the right ventricle; 2) The pulmonary valve regulates blood flow from the right ventricle into the pulmonary arteries; 3) the mitral valve regulates blood flow from the left atrium to the left ventricle; and 4) The aortic valve regulates blood flow from the left ventricle to the aorta.
Electrical signals in your heart muscle cause your heart to contract. The electrical signals begin in the sinoatrial (SA) node (at the top of the right atrium). The SA node is sometimes called the heart’s natural pacemaker. The electrical signals travel through the muscle fibers of the heart causing the atria and ventricles to contract.