About the heart
Composed of the heart and blood vessels, the cardiovascular system is responsible for circulating blood throughout the body. Blood contains nutrients and oxygen used by the organs. A healthy cardiovascular system is vital to ‘feed’ the body with the fuel it needs to work.
The heart is the hardest working muscle in the human body. It acts as a complex pump made up of strong muscle tissue. Located almost in the center of the chest, the heart of a child is about the size of their fist. Each contraction of the heart is called a beat. Each beat sends nutrients and oxygen throughout the body providing fuel for the organs.
During an average lifetime, the human heart beats more than three billion times — pumping an amount of blood that equals about one million barrels. The heart is always working, 24 hours a day, seven days a week — even while we are sleeping. A child's heart works just as hard as an adult's heart. In fact, a baby’s heart may beat up to 190 times a minute, while an adult's heart usually beats between 60 and 100 times a minute. The rate at which the heart pumps gradually slows down from birth to adolescence.
Design of the heart
The heart is made up of four compartments called chambers; two on top, and two below. The top two chambers of the heart are called the left atrium and the right atrium. The left atrium receives blood from the lungs. The right atrium receives blood back from the body via the inferior and superior vena cava. The two chambers on the bottom are called the ventricles. They pump blood into the body and lungs.
Blood flow
"Used" blood from the body is pumped into the 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 to the atrium. The superior vena cava brings blood to the heart 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 receives 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 throughout the body. In the middle of the heart is the septum, a thick muscle that separates the left and right side of the heart.
Blood vessels
Blood vessels bring blood to the lungs (where oxygen enters the bloodstream) and is then distributed to the body.
- The inferior and superior venae cavae bring oxygen-poor (blue) blood from the body into the right atrium.
- The pulmonary artery channels oxygen-poor (blue) blood from the right ventricle into the lungs, where oxygen enters the bloodstream.
- The pulmonary veins bring oxygen-rich (red) blood to the left atrium.
- The aorta channels oxygen-rich (red) blood to the body.
A network of arteries and veins also carry blood throughout the body.
- Arteries transport blood from the heart to the body tissues.
- Veins carry blood back to the heart.
Heart valves
The direction of the flow of blood to and from the heart is controlled by a series of valves. These valves are made up of flaps called leaflets that only allow the blood to flow in one direction. Normal valves have three flaps (leaflets), except the mitral valve, which only has two flaps. The heart has four valves connecting each chamber to the blood supply. These four valves are the:
- Tricuspid valve - located between the right atrium and the right ventricle.
- Pulmonary valve - located between the right ventricle and the pulmonary artery.
- Mitral valve - located between the left atrium and the left ventricle.
- Aortic valve - located between the left ventricle and the aorta.