Picture 3.1 A heart in the chest cavity of a person having open heart surgery. The heart is beating.
Your heart beats without fail all day every day. A healthy person's heart runs at about 72 beats per minute when they are resting. That's over 100 thousand beats in a day and over 2 billion in a lifetime.
The heart muscle is extremely efficient and it can be regulated to meet the demands of the body. Your heart rate goes up during activity to supply more blood to hard-working muscles.
Click here to listen to a normal heart and one type of abnormality. (These sound files are a total of 75 K).
Know your heart inside and out
Diagrams are drawn as if the heart is being looked at from the front. This can be confusing as the heart's left side actually appears on the right.
The coronary arteries are extremely important because they provide the heart muscles with a good supply of blood. If they are narrowed or blocked, for example by having too much fat in the diet, it can cause a heart attack (see page 6).
Picture 3.2 The heart inside and out. Click here to see an animation of the heart.
The large blood vessels carry blood to and from the heart's pumps. The aorta is the main artery from the heart. It carries oxygenated blood to the body and head. Deoxygentated blood returns to the heart in the vena cava. This blood is sent to the lungs along the pulmonary arteries to collect oxygen. It returns through the pulmonary veins.
Looking inside the heart there are four chambers. At the top, the right atrium receives blood coming from the body and the left atrium collects blood coming from the lungs. The ventricles are underneath the atria and are the chambers that pump blood out of the heart. The blood flow in and out of the ventricles is controlled by four valves. These ensure that blood always comes in from the atria and flows out through an artery.
The right ventricle has a thin wall because it only needs to pump the blood around the lungs at low pressure. The left ventricle however has a much thicker wall because it generates the high pressure needed to push blood to the head and body.
One-way valves between the chambers stops blood from flowing in the wrong direction when the heart contracts. Sometimes they become damaged and cause the blood to flow irregularly. This can cause heart failure so valves can be replaced with artificial ones.
We all start with a "hole" in the heart. Before birth, a lot of the blood is diverted from the right to left atrium through an opening between the two chambers. This is because the lungs are not used for breathing in the uterus (womb). Usually the "hole" closes over just before birth but in some babies this does not happen and an operation may be need to seal it.
Picture 3.3 Do question 3 to get all the labels in place.
