About your heart

What does the heart do? The heart is a muscle about the size of a closed fist. The heart usually beats about 60 - 100 times per minute. With each beat, your heart pushes blood throughout your body. Blood doesn't flow on its own; it needs the heart to beat (contract) and push the blood through your blood vessels.

Each time your heart beats, your muscle is contracting. You might not think of you heart as a muscle that gets a big workout - but it does. Think about what your heart does every day in a healthy adult:

  • It pumps about 1,900 gallons (7,200 liters) of blood.
  • It beats 100,000 times.
  • And it gets only a fraction of a second to rest between each beat!

The term cardiac refers to the heart. Your heart's walls are made mostly of strong muscle called the myocardium. The myocardium is the strongest, hardest- working muscle in your body. It had to be- your heart pumps blood from your head to your toes. None of your tissues or organs could survive without the oxygen and nutrients carried by your blood.

Heart Chambers:

What do the heart chambers do?

The inside of your heart is divided into four sections, or chambers. The chambers are like separate rooms that hold the blood before pumping it out to the body. Each chamber has doors (valves) that let blood pass in and out.

The Atria- Receiving blood from the body

The two upper chambers in your heart are called the atria. (Just one of these chambers is called the atrium.) When blood flows into your heart from the body or lungs, it always flows into either the right or left atrium. When blood flows into your heart and lungs, it always flows into either the right or left atrium.  When blood flows into your heart from the lungs, it always flows into the left atrium. Blood flows into both atria at the same time. When the atria are both full with blood, they contract and push blood down into the ventricles at the same time.

The ventricles- Pumping blood out to the body

The two lower chambers in your heart are called the ventricles. The ventricles are known as the pumping chambers of your heart. When blood leaves your heart to go to your lungs, it is always pumped out from your right ventricle. When blood leaves your heart to go to the rest of your body, it is always pumped out from the left ventricle. The ventricles are larger than the atria. The ventricles are also very strong because they have to pump hard enough to push blood throughout your entire body.

Your heart's right and left sides.

Sometimes the right and left sides of your heart are called your heart and left heart. The right atrium and right ventricle are, of course, on the right side of your heart. (it's the same side as your right arm) The left atrium and the left ventricle are on the left side of your heart. However, if you took a picture of the heart, the right heart is on the left.

A wall called the septum separates the right and left sides of your heart. The septum also separates the oxygen- rich blood from the oxygen- poor blood in your heart. Blood that hasn't yet been to the lungs (oxygen-poor blood) stays on the right side of the septum. Blood returning from the lungs (oxygen-rich blood) stays on the right side of the septum. Blood returning from the lungs (oxygen-rich blood) stays on the left side of the septum.

Heart Valves:

What do you heart valves do?

Your heart has four valves that act like doors. Each valve has two jobs. They open to allow blood to flow in or out. They close to prevent blood from flowing where it shouldn't flow. The heart valves keep blooding flowing in one direction through your heart.

Circulatory System (Blood Flow)

What does it do?

Your circulatory system continuously delivers blood to all parts of your body, it also returns oxygen-poor blood to the lungs. The circulatory system consists of your:

  • Heart, which pumps blood into blood vessels
  • Blood vessels, a system of tubes that carry blood to your entire body and back to your heart
  • Lungs, which supply oxygen to the blood

You can compare your circulatory system to a "figure eight". One loop routes blood from the heart to the lungs and back to the heart. On this loop, carbon dioxide is removed from your blood, and oxygen is put into the blood. You fill your lungs with oxygen when your breathe in- and carbon dioxide is removed when you breathe out.

The second loop delivers blood- along with oxygen and nutrients- to every other part of your body. The blood vessels then take away waste products (for example, carbon dioxide). Finally, the oxygen-poor blood returns to the heart for more oxygen. The cycle then repeats continuously.

This second loop is large and very complex. To give you an idea, an adult has 60,000 miles (96,560 kilometers) of blood vessels throughout the body!

Your circulatory system does more than carry oxygen and carbon dioxide, however. It carries nutrients from your intestines to your body's tissue. It carries hormones to appropriate parts of your body from your glands. The circulatory system also carries waste product to your liver and kidneys to be removed.

Blood vessels

What do blood vessels do?

Your blood vessels are a vast network of tubes that carry blood throughout your entire body. The blood vessels "drop off" oxygen and nutrients to all of the cells in your body. The blood vessels then "pick up" waste products like carbon dioxide- and return the oxygen-poor blood to your heart and lungs. When the blood passes through your lungs, oxygen moves once again into the blood.

You might sometimes hear the terms vascular or vasculature. These terms refer to your blood vessels.

Types of blood vessels

Three types of blood vessels carry blood through your body: arteries, capillaries, and veins.


Arteries carry blood rich in oxygen from your heart to the tissues and organs in your body like your brain, kidneys, and liver. Because arteries carry oxygen, they appear red. Artery walls are thick and flexible - and they need to be. The heart pumps with enough force,or pressure, to deliver blood throughout the body. The thicker walls help protect the arteries against damage from the high pressure.

(Here's a good tip to remember the difference between the arteries and the veins. The "a'' in artery can also refer to the blood being carried "away" from your heart.)

Arteries get smaller as they get farther from your heart. At their smallest point, arteries become capillaries.

Capillaries are the body's tiniest blood vessels. They carry blood from every cell in your body. In an adult, that amounts to trillion of cells. Capillaries are when the "exchange" takes place. Capillary walls are so thin that oxygen and nutrients can pass right through them into your body's cells. Waste products from the cells, like carbon dioxide, can also pass through the capillary walls and into your blood stream before returning to the heart. Capillaries connect arteries to veins.


Capillaries get larger as they leave each cell and soon become veins. Veins carry the oxygen-poor blood back to your heart. Because they carry blood without oxygen, veins appear blue. Vein walls are much thinner than artery walls. That's because blood flows through them at a lower pressure. The word venous refers to veins.

Blood vessels in your heart

Like the other muscles in your body, your heart needs oxygen to survive. The blood vessels that deliver oxygen to your heart muscle are the coronary arteries. They have that name because they encircle and sit on the surface of your heart like a crown. (The word "coronary" means crown.)

The coronary arteries are divided into two systems. The left coronary artery system supplies blood mostly to the left side of your heart. The right coronary artery supplies blood mostly to the right side of your heart.

Commonly blocked coronary arteries

Maybe someone your know has coronary artery disease (CAD), or heart disease. A person with CAD has at least one coronary artery that's clogged with plaque. Plaque results when fatty substances, like cholesterol, build up in your arteries.  Over time, the arteries become hard and narrowed. In the coronary arteries, plaque can buildup and slow blood flow to the heart muscle.

These larger coronary arteries are the ones that are most likely to become blocked or affected by CAD

  • Left anterior descending artery
  • Left circumflex artery
  • Left main artery
  • Posterior descending artery
  • Right coronary artery

Coronary veins

Coronary veins are found in only your heart. And like other veins in your body, coronary veins carry oxygen-poor blood. Coronary veins collect the oxygen-poor blood from your heart muscle of the heart wall.

Coronary veins empty blood directly into the right atrium through the coronary sinus. The coronary sinus is a small opening in the right atrium that's protected by a flap of tissue.

Blood vessels outside your heart

Peripheral vascular system

Outside your heart, blood vessels deliver oxygen and nutrients to the rest of your body. These blood vessels make up the peripheral vascular system.

Commonly blocked peripheral arteries

Like the heart's coronary arteries, peripheral arteries can become clogged with plaque. Plaque results when fatty deposits, like cholesterol, build up in your arteries. Over time, the arteries can become hard and narrowed. In the peripheral arteries, this plaque can slow blood flow to vital areas such as the brain.

This problem with blocked arteries is called peripheral vascular disease (PVD). You may also hear it called peripheral artery disease. Some of the arteries that are especially prone to PVD supply blood to your:

  • Brain (the carotid arteries, located in your neck)
  • Arms (the subclavian arteries)
  • Kidneys (the renal arteries)
  • Lower abdomen (the femoral arteries)
  • Lower legs (the popliteal arteries)

Vessels used for bypasses

If you have a blocked artery, your doctor may fix the problem by re- routing the blood through part of a healthy blood vessel. A section of healthy blood vessel is often taken from your chest, arm, or leg. Your doctor sews- or "grafts" one end of the healthy blood vessel below the blocked artery. The doctor then grafts the other end of the healthy blood vessel above the blocked artery. Blood flows through the new blood vessel around the blockage. This "detour" is called a bypass graft.

Your doctor chooses which blood vessels to use for a graft. That choice depends on the size and location of your blocked artery - and on the size of your other blood vessels available for grafts. Doctors usually choose from among these three options when taking the healthy vessel for the graft:

  • Internal mammary artery- from inside the chest wall
  • Radial artery- which runs from your elbow to your wrist
  • Saphenous vein- which runs the length of your leg