MHVI Owners Manual . Anatomy . Your Heart

The centerpiece of your cardiovascular system is your heart, which is located in the center of your chest and is protected by the rib cage and breast bone (sternum). The heart is the size of the average human fist and is shaped somewhat like an upside-down pear. Every day this incredible organ beats more than 100,000 times as it pumps more than 2,000 gallons of blood through your body.

Your heart is a muscular pump that is divided into two sides. The right side of your heart receives oxygen-depleted blood from the body and sends this "used" blood to the lungs to be re-oxygenated. The left side of your heart receives the "fresh" oxygen-rich blood from the lungs and pumps it through your body.

Each side of your heart has two compart-ments or chambers. Therefore, your heart has a total of four chambers. The upper chamber of each side of your heart is called the atrium and the lower chamber is called the ventricle. The atria (plural for atrium) are receiving chambers for blood returning to the heart from the lungs and body. The ventricles, the more muscular pumping chambers, send the blood to the body or lungs. The left and right side of your heart are separated from one another by a muscular wall called the septum (see illustration). With each heartbeat, the squeezing action of the left ventricle normally forces 60 to 70 percent of the blood it contains into your blood vessels. This percentage is known as the ejection fraction of the left ventricle.

The muscle that forms your heart actually has three layers: the outermost and toughest layer is the pericardium; the middle, muscular layer is the myocardium; and the thin, inner layer is the endocardium. Because the left ventricle pumps blood through your entire body, its muscular wall is thicker than the wall of the right ventricle, which pumps blood to the lungs.

Do you know what your ejection fraction is?

With each heartbeat, the squeezing action of the left ventricle normally forces 60 to 70 percent of the blood it contains into your blood vessels. This percentage is known as the ejection fraction of the left ventricle.

Four valves, located within the heart, help direct the flow of blood through your heart. These valves act as one-way doors, opening to allow blood to flow in the right direction and shutting to prevent blood from flowing in the wrong direction. When listening to your heart, your doctor can actually hear the valves as they close. If a valve is not functioning properly, a special sound called a murmur can often be heard.

Your heart works efficiently because it contracts or beats in a regular, rhythmic pattern. Both atria fill with blood and contract, pushing blood into the ventricles. Then both ventricles contract, sending blood to the lungs and body in a rhythm that creates a continuous "recycling" of your blood. This process, which moves your blood simultaneously through all the chambers of your heart, occurs 24-hours a day, every day of your life. The process is described below. It is also shown in the illustration below.

Blood Flow Through the Heart

"Used" blood that has already traveled through the body and is low in oxygen and high in waste products returns to the heart through the veins and enters the right atrium.
The "used" blood passes through the tricuspid valve into the right ventricle.
The right ventricle then pumps the blood through the pulmonic valve (3a) to the lungs through the pulmonary arteries (3b).
This blood receives oxygen from the lungs and passes through the pulmonary veins into the left atrium.
The oxygen-rich blood passes from the left atrium through the mitral valve into the left ventricle.
This "fresh" blood is pumped by the left ventricle through the aortic valve out to the body to begin the cycle again.