What is the heart?
The heart is a fist-sized organ that pumps blood throughout your body. It's the primary organ of your circulatory system.
Your heart contains four main sections (chambers) made of muscle and powered by electrical impulses. Your brain and nervous system direct your heart’s function.
What does a heart diagram look like?
The inside and outside of your heart contain components that direct blood flow:
Inside of the Heart
Outside of the Heart
What is the heart’s function?
Your heart’s main function is to move blood throughout your body. Your heart also:
- Controls the rhythm and speed of your heart rate.
- Maintains your blood pressure.
How does your heart work with other organs?
Your heart works with other body systems to control your heart rate and other body functions. The primary systems are:
- Nervous system: Your nervous system helps control your heart rate. It sends signals that tell your heart to beat slower during rest and faster during stress.
- Endocrine system: Your endocrine system sends out hormones. These hormones tell your blood vessels to constrict or relax, which affects your blood pressure. Hormones from your thyroid gland can also tell your heart to beat faster or slower.
Where is your heart located?
Your heart is located in the front of your chest. It sits slightly behind and to the left of your sternum (breastbone). Your ribcage protects your heart.
What side is your heart on?
Your heart is slightly on the left side of your body. It sits between your right and left lungs. The left lung is slightly smaller to make room for the heart in your left chest.
How big is your heart?
Everyone’s heart is a slightly different size. Generally, adult hearts are about the same size as two clenched fists, and children’s hearts are about the same size as one clenched fist.
How much does your heart weigh?
On average, an adult’s heart weighs about 10 ounces. Your heart may weigh a little more or a little less, depending on your body size and sex.
What are the parts of the heart’s anatomy?
The parts of your heart are like the parts of a house. Your heart has:
- Chambers (rooms).
- Valves (doors).
- Blood vessels (plumbing).
- Electrical conduction system (electricity).
Your heart walls are the muscles that contract (squeeze) and relax to send blood throughout your body. A layer of muscular tissue called the septum divides your heart walls into the left and right sides.
Your heart walls have three layers:
- Endocardium: Inner layer.
- Myocardium: Muscular middle layer.
- Epicardium: Protective outer layer.
The epicardium is one layer of your pericardium. The pericardium is a protective sac that covers your entire heart. It produces fluid to lubricate your heart and keep it from rubbing against other organs.
Your heart is divided into four chambers. You have two chambers on the top (atrium, plural atria) and two on the bottom (ventricles), one on each side of the heart.
- Right atrium: Two large veins deliver oxygen-poor blood to your right atrium. The superior vena cava carries blood from your upper body. The inferior vena cava brings blood from the lower body. Then the right atrium pumps the blood to your right ventricle.
- Right ventricle: The lower right chamber pumps the oxygen-poor blood to your lungs through the pulmonary artery. The lungs reload blood with oxygen.
- Left atrium: After the lungs fill blood with oxygen, the pulmonary veins carry the blood to the left atrium. This upper chamber pumps the blood to your left ventricle.
- Left ventricle: The left ventricle is slightly larger than the right. It pumps oxygen-rich blood to the rest of your body.
Your heart valves are like doors between your heart chambers. They open and close to allow blood to flow through.
The atrioventricular (AV) valves open between your upper and lower heart chambers. They include:
- Tricuspid valve: Door between your right atrium and right ventricle.
- Mitral valve: Door between your left atrium and left ventricle.
Semilunar (SL) valves open when blood flows out of your ventricles. They include:
- Aortic valve: Opens when blood flows out of your left ventricle to your aorta (artery that carries oxygen-rich blood to your body).
- Pulmonary valve: Opens when blood flows from your right ventricle to your pulmonary arteries (the only arteries that carry oxygen-poor blood to your lungs).
Your heart pumps blood through three types of blood vessels:
- Arteries carry oxygen-rich blood from your heart to your body’s tissues. The exception is your pulmonary arteries, which go to your lungs.
- Veins carry oxygen-poor blood back to your heart.
- Capillaries are small blood vessels where your body exchanges oxygen-rich and oxygen-poor blood.
Your heart receives nutrients through a network of coronary arteries. These arteries run along your heart’s surface. They serve the heart itself.
- Left coronary artery: Divides into two branches (the circumflex artery and the left anterior descending artery).
- Circumflex artery: Supplies blood to the left atrium and the side and back of the left ventricle.
- Left anterior descending artery (LAD): Supplies blood to the front and bottom of the left ventricle and the front of the septum.
- Right coronary artery (RCA): Supplies blood to the right atrium, right ventricle, bottom portion of the left ventricle and back of the septum.
Electrical conduction system
Your heart’s conduction system is like the electrical wiring of a house. It controls the rhythm and pace of your heartbeat. It includes:
- Sinoatrial (SA) node: Sends the signals that make your heart beat.
- Atrioventricular (AV) node: Carries electrical signals from your heart’s upper chambers to its lower ones.
Your heart also has a network of electrical bundles and fibers. This network includes:
- Left bundle branch: Sends electric impulses to your left ventricle.
- Right bundle branch: Sends electric impulses to your right ventricle.
- Bundle of His: Sends impulses from your AV node to the Purkinje fibers.
- Purkinje fibers: Make your heart ventricles contract and pump out blood.
Conditions and Disorders
What conditions and disorders affect the human heart?
Heart conditions are among the most common types of disorders affecting people. In the United States, heart disease is the leading cause of death for people of all genders and most ethnic and racial groups.
Common conditions that affect your heart include:
- Atrial fibrillation (Afib): Irregular electrical impulses in your atrium.
- Arrhythmia: A heartbeat that is too fast, too slow or beats with an irregular rhythm.
- Cardiomyopathy: Unusual thickening, enlargement or stiffening of your heart muscle.
- Congestive heart failure: When your heart is too stiff or too weak to properly pump blood throughout your body.
- Coronary artery disease: Plaque buildup that leads to narrow coronary arteries.
- Heart attack (myocardial infarction): A sudden coronary artery blockage that cuts off oxygen to part of your heart muscle.
- Pericarditis: Inflammation in your heart’s lining (pericardium).
How can I keep my heart healthy?
If you have a condition that affects your heart, follow your healthcare provider’s treatment plan. It’s important to take medications as prescribed.
You can also make lifestyle changes to keep your heart healthy. You may:
- Achieve and maintain a healthy weight for your sex and age.
- Drink alcohol in moderation.
- Eat a heart-healthy diet with plenty of fruits, vegetables and whole grains.
- Exercise moderately for at least 150 minutes per week.
- Limit your sodium intake.
- Manage your stress with healthy strategies like meditation or journaling.
- Quit smoking and/or using tobacco products and avoid secondhand smoke.
Frequently Asked Questions
What should I ask my doctor about my heart?
You may want to ask your healthcare provider:
- How does my family history affect my heart health?
- What can I do to lower my blood pressure?
- How do my cholesterol levels affect my heart?
- What are the symptoms of a heart attack?
- What foods should I eat to prevent heart disease?
A note from Cleveland Clinic
Your heart is the primary organ of your circulatory system. It pumps blood throughout your body, controls your heart rate and maintains blood pressure. Your heart is a bit like a house. It has walls, rooms, doors, plumbing and an electrical system. All the parts of your heart work together to keep blood flowing and send nutrients to your other organs. Conditions that affect your heart are some of the most common types of conditions. Ask your healthcare provider how you can improve your heart health.