How the Heart Works

In order to understand a pediatric heart transplant, it is helpful to know how the heart works normally. The heart is a muscular organ in the middle of the chest. A child’s heart is about the size of his fist.

The heart has four chambers:

  • The two upper chambers are the right atrium and the left atrium.
  • The two lower chambers are the right ventricle and the left ventricle.

The heart is separated lengthwise into the right and left sides by a wall called the septum. Four one-way valves control the flow of blood through the heart.

How the Heart Works
Illustration Copyright©2006 Nucleus Medical Art, All rights reserved.

What Does the Heart Do?

The heart is a complex organ with many functions. A primary function of the heart is to pump oxygen-rich blood to vital organs and tissues. Every cell of the body needs oxygen for energy and for life.

Step 1

Blood comes to the right side of the heart through two large veins, the superior vena cava and the inferior vena cava. This is blood that has been “used” by the body. It contains very little oxygen and also contains “waste" in the form of carbon dioxide.

Step 2

The blood then passes through the tricuspid valve to the right ventricle. From here, it is pumped out through the pulmonary valve and pulmonary artery to the lungs.

Step 3

In the lungs, the carbon dioxide is removed from the blood. It is exchanged for oxygen that has been breathed in through the nose and mouth.

Step 4

The oxygen-rich blood leaves the lungs and returns to the left atrium through the pulmonary veins. This process is called pulmonary circulation. The word “pulmonary” means lungs.

Step 5

Blood flows from the left atrium through the mitral valve into the left ventricle. The left ventricle is a thick, powerful muscle.

Step 6

The left ventricle pumps oxygen-rich blood through the aortic valve to the aorta and out through the body. This is the way a child’s body and organs receive blood and oxygen.

The heart repeats this cycle of receiving and pumping blood to a child’s body many times a minute. This is called the heart rate or “pulse.”

Just as a child’s tissues need oxygen-rich blood for energy, his heart needs its own blood supply for energy. The coronary arteries are blood vessels that wrap around the heart and supply it with oxygenated blood.