How Your Heart Works
The heart is the hardest-working muscle in your body. An average adult heart is about the size and shape of a closed fist. The main job of your heart is to pump blood. This section will show how the heart and blood vessels keep your body healthy.
Although you may feel your heart beat when you place your hand over it, your heart is not right under your skin. Instead, your heart is behind your breastbone, inside your ribcage, and between your lungs.
- Each minute about 5 quarts (4.7 liters) of blood flow through your heart.
- Each day the average heart beats 100,000 times and pumps about 1900 gallons (7200 liters) of blood.
- In a 70-year lifetime, an average human heart beats more than 2.5 billion times.
The hollow center of your heart has four sections, called chambers. Each chamber is like a separate room, with doors that let blood in and out.
- Two upper chambers are called atria; one is an atrium. The atria are the receiving chambers of the heart.
- Two lower chambers are called ventricles. The ventricles are the pumping chambers of the heart.
When you listen to your heartbeat through a stethoscope ("lubb-dubb, lubb-dubb"), you hear the sound of your heart valves closing.
Your heart valves keep blood flowing in one direction through your heart, just like the one-way valves in your home's plumbing. They open to let blood flow through, and then close to prevent blood from flowing back the way it came. Blood flows through each valve one time on its way through your heart.
The four valves can be grouped by their job:
- The tricuspid valve is between the right atrium and the right ventricle.
- The mitral valve is between the left atrium and the left ventricle.
- Blood flows out of the right ventricle to the lungs through the pulmonary valve.
- Blood flows out of the left ventricle to your body through the aortic valve.
Blood flows to and from the heart through tubes called blood vessels. Blood vessels carry blood to every part of your body, "dropping off" oxygen and nutrients and "picking up" waste products and carbon dioxide. Then the blood returns to the heart. There are three types of blood vessels, arteries, capillaries and veins.
Arteries always carry blood flowing away from the heart. Major arteries connected to your heart include:
The pulmonary artery carries blood pumped from the right side of the heart to the lungs to pick up a fresh supply of oxygen.
- The aorta is the main artery that carries oxygen-rich blood pumped from the left side of the heart out to the body.
- The coronary arteries carry oxygen-rich blood from the aorta to the heart muscle itself. The heart needs its own blood supply to function.
Capillaries are the tiniest vessels in the body, carrying blood to and from every cell in your body.
Veins are major blood vessels that carry the oxygen-poor blood from the body back to your heart.
Like coronary arteries, coronary veins work just in your heart. Coronary veins collect the oxygen-poor blood from your heart muscle—from the heart wall, not from inside the heart chambers. The coronary veins empty blood directly into the right atrium.
Someone you know may have coronary artery disease (CAD). A person with CAD has at least one coronary artery that is clogged and is not letting all the blood through to the heart muscle.
Outside your heart, blood delivers oxygen and nutrients to the rest of your body. These blood vessels make up the peripheral artery system.
Just like coronary arteries, peripheral arteries can become clogged and slow blood flow to vital areas, such as your brain or kidneys. This problem is called peripheral artery disease (PAD). Some arteries are more prone to PAD than others, including:
- The aorta, your body's largest artery, is attached directly to the left ventricle of your heart. The left ventricle pumps blood out of your heart through the aortic valve into the aorta. All other major arteries branch from the aorta and carry blood to the rest of your body.
- The carotid arteries are the main arteries in your head and neck that supply blood to your brain.
- The subclavian arteries supply blood to your arms.
- The renal arteries supply blood to your kidneys.
- The iliac arteries supply blood to your lower abdomen.
- At the pelvis, the iliac arteries become the femoral arteries, which supply blood to most of your legs.
- At your knees, the femoral arteries become the popliteal arteries, which supply blood to your lower legs.
- At your ankles, the tibial arteries, which supply blood to your feet.
Your blood pressure is a measure of the force of your blood pushing against the walls of your arteries. Blood pressure is measured in two numbers—a bigger (higher) number "over" a smaller (lower) number.
- The number on top is called the systolic pressure. It is a measure of the pressure when your heart is squeezing.
- The number on the bottom is called the diastolic pressure. It is a measure of the pressure when your heart is resting between beats.
Normal blood pressure for an adult is “120 over 80” or 120/80 mmHG (millimeters of mercury).
Blood pressure tells your doctor how hard your heart is working. If one or both numbers are higher than normal, you have high blood pressure. High blood pressure means your heart is working extra hard to push blood through your arteries. It also means you may be at higher risk for developing heart problems or disease.
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