The Normal Heart

It is important to understand your child’s heart problem and how it affects him. An easy way to gain this understanding is to review how the normal heart works. The next several paragraphs define the structures of the heart and explain how blood circulates through the body.

The heart is a strong muscle that acts as a pump. The size of the heart is nearly equal to its “owner’s” fist. The heart’s pumping action causes the heartbeat or pulse. The heart pumps blood high in oxygen (red blood) to the body. After the body uses the oxygen, the blood low in oxygen (blue blood) is returned to the heart. Blue blood then is pumped through the lungs to pick up more oxygen. This process is repeated over and over again.

The diagram shows how blood passes through the heart. The heart is divided into four chambers: the left and right atria (upper chambers) and the left and right ventricles (lower chambers). The wall that separates the right side of the heart from the left side is called the septum.

Blue blood returns from the body into the right atrium and then flows into the right ventricle. The right ventricle pumps blood into the pulmonary arteries. From the pulmonary arteries, blood passes into tiny vessels in the lungs where it picks up oxygen and becomes red. Red blood returns to the left atrium and flows into the left ventricle. The left ventricle pumps blood into the aorta that carries it to the body.

As blood moves in and out of the heart’s chambers, it passes through four small flap-like structures called valves. With each heartbeat, the valves act as one-way doors that open and close so blood will flow in the proper direction. When a valve is closed, no blood passes through it. There are two valves on each side of the heart. The tricuspid and pulmonary valves are on the right side. The mitral and aortic valves are on the left side.

Blood travels to and from the heart in two types of blood vessels. As blood containing oxygen (red blood) is pumped from the heart to the body, it travels through vessels called arteries. After the body has used the oxygen, the blood without oxygen (blue blood) is returned to the heart in blood vessels called veins.

As red blood is pumped from the heart to the rest of the body, pressure is generated in the arteries (blood vessels). This pressure is commonly measured as blood pressure. The pressure in the arteries when the heart muscle contracts (squeezes) is called the systolic blood pressure. The pressure in the arteries when the heart muscle is relaxed is called the diastolic blood pressure.

The heart is made of three types of tissue. The large muscle layer of the heart is called the myocardium. The thin tissue that covers the inside of the heart is called the endocardium. The entire heart rests in a thin elastic-like sac called the pericardium.