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About the Heart

How Does the Heart Work?

The heart is about the same size as a clenched fist. Its main function is pumping blood to all the tissues in the body. The heart muscle, called the myocardium, is the pumping force, but the heart could not function without the valves, coronary arteries and the conduction system.

The heart is divided into four hollow cavities. The upper cavities are receiving chambers, called the atria (singular is atrium), and the lower cavities are pumping chambers, called the ventricles. The atria and ventricles on the right side are separated from those on the left by a septum.

The right atrium receives blood from the upper and lower halves of the body via two large veins, the superior vena cava and inferior vena cava. This blood is low in oxygen and high in carbon dioxide. The right atrium sends blood to the right ventricle. The right ventricle pumps blood into the pulmonary artery to circulate through the lungs in order to release carbon dioxide and receive oxygen.

The left atrium receives the returning oxygen-rich blood from the pulmonary veins. It sends blood to the left ventricle, which pumps blood through the aorta to all tissues and organs. The left ventricle must have enough strength to pump this blood throughout the body. Therefore, it is stronger and more muscular than the right ventricle.

What is a coronary artery?

The heart muscle has its own blood supply which carries oxygen, and nutrients to the myocardium. It receives this blood supply through the right and left coronary arteries, through openings at the origin of the aorta.

The left main coronary artery divides into the left anterior descending (LAD) artery and the circumflex artery. The LAD carries blood down the front of the heart to both (primarily the left) ventricles. The circumflex winds around the back of the heart. The right coronary artery supplies blood to most of the right ventricle and a portion of the back of the left ventricle. Each of these arteries branch into smaller vessels to penetrate the heart muscle. Each individual person has a unique coronary artery tree. The number and placement of branches can vary greatly.

What is the conduction (electrical) system of the heart?

The normal beating of the heart is vital to effective pumping of blood. A heart beat is controlled by its conduction system. The conduction system is clumps and strands of specialized cardiac muscle tissue that initiate and distribute impulses that stimulate the heart to contract and pump blood through the body. If the heart beat is interrupted or erratic, the heart may not pump effectively.

The sinus node is a group of cells in the upper part of the right atrium. The sinus node is the heart's natural pacemaker and the normal origin of the electrical impulse. The electrical impulse then passes to the atrioventricular node. The atrioventricular node (AV node) is a cluster of cells between the right atrium and ventricle. It acts like a gate to slow down the electrical current before it passes to the ventricles. This process allows the atrium to contract before the following ventricular contraction.

After passing through the AV node, the current will travel into specialized conduction tissue called the HIS-Purkinje system. This system distributes the electrical impulse throughout the muscle cells of the left and right ventricles, resulting in contraction of the ventricles.

A normal heart rate in a resting adult is between 60 and 100 beats per minute. Exercise, mental stress, tobacco, caffeine, alcohol and certain prescription and nonprescription drugs can increase the heart rate. Additionally, sleep and other medications can slow the heart rate.

What is Heart Disease?

Heart disease can involve any and all parts of the cardiovascular system. It can affect the myocardium (the heart muscle), the coronary arteries, the heart valves, the conduction system, and the pericardium (the sac surrounding the heart).

Among the largest programs in the nation, CVTSA surgeons perform more than 1,000 cardiac operations each year.


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