What is the heart?
The heart is a hollow organ made of muscle. The heart and blood vessels Biology of the Blood Vessels Blood vessels are hollow tubes like pipes that carry blood through your body. The blood delivers oxygen and nutrients to all parts of your body and removes waste products, such as carbon dioxide... read more are part of your cardiovascular system.
Blood carries oxygen and nutrients to all parts of your body
Your heart has to beat constantly through your whole life and never gets a rest
Every minute, your heart beats about 70 times and pumps about 1 gallon (4 liters) of blood. Your heart beats faster and pumps harder during exercise, when your body needs more oxygen. When you check your pulse, you're measuring your heart rate, or the number of beats per minute.
Blood traveling through your body delivers oxygen and nutrients to tissues and organs. Waste from those tissues and organs is carried by blood to the lungs and kidneys for removal from the body.
How does the heart work?
The heart is a pump for blood. It's actually 2 pumps connected together—one on the right side of the heart and one on the left side.
The pump on the right side gets blood from your body and pumps it through your lungs where it picks up oxygen
The pump on the left side gets oxygen-filled blood from your lungs and pumps it throughout your body
In order to pump blood, your heart has:
Four hollow spaces (chambers) for the blood to flow through
Four heart valves to make sure blood flows in the right direction
An electrical system to tell the heart muscle when to contract
Blood vessels to feed the heart muscle itself
A Look Into the Heart
This cross-sectional view of the heart shows the direction of normal blood flow.
What are the heart chambers?
The heart has 4 compartments (chambers), two on the right and two on the left. The chambers of your heart relax, fill with blood, and then contract to pump the blood out.
The two upper chambers (the right atrium and left atrium) let blood into the heart
The two lower chambers (the right and left ventricles) pump blood out
What are heart valves for?
Your heart has 4 valves that control the flow of blood. The valves open to let blood out of one chamber and into the next chamber or blood vessel. The valves close to keep blood from flowing backward into the wrong chamber.
When you put your head on someone's chest and listen to their heartbeat, you're hearing the sound of the heart valves opening and closing.
What is the heart's electrical system?
Your heart should always have a regular, rhythmic beat, like the ticking of a clock:
Your heart rhythm is controlled by pacemaker cells in your heart
Pacemaker cells send out regular electrical signals to your heart muscle to make it contract
The signals are carried through tissue called the conduction system
There are special pacemaker cells in a part of your heart called the SA node. The pacemaker cells have their own natural rhythm of 60 to 100 signals per minute. Nerves from your brain can send messages to the cells telling them to speed up or slow down.
Your heart's conduction system has tiny strips of tissue sort of like electrical wires. The conduction system carries the pacemaker signals to the rest of your heart. The conduction system includes a gateway called the AV node. The AV node controls how signals pass from the upper chambers of your heart (atria) to the lower chambers (ventricles). When the conduction system is working properly, the signals get to each of your heart muscle cells at just the right time. Your heart then gives a good, strong beat that pumps blood properly.
Tracing the Heart’s Electrical Pathway
The sinoatrial (sinus) node (1) initiates an electrical impulse that flows through the right and left atria (2), making them contract. When the electrical impulse reaches the atrioventricular node (3), it is delayed slightly. The impulse then travels down the bundle of His (4), which divides into the right bundle branch for the right ventricle (5) and the left bundle branch for the left ventricle (5). The impulse then spreads through the ventricles, making them contract.
Why does the heart need blood vessels?
Like all muscles, the heart needs a steady supply of blood to work. You might think that, because the heart is full of blood, it doesn't need a separate blood supply. However, blood that pumps through the heart doesn't feed the heart muscle. Instead the heart muscle is fed by its own blood vessels.
The heart's blood vessels are called coronary arteries
Coronary is a word for heart.
What can go wrong with the heart?
You can have problems with any part of your heart:
The muscles of the heart chambers can pump too weakly causing heart failure Heart Failure Your heart pumps blood to carry oxygen and nutrients to the rest of your body. Heart failure is when your heart doesn’t pump blood as well as it should. It doesn’t mean your heart has stopped... read more
In heart valve disorders Overview of Heart Valve Disorders Your heart is a muscle that pumps blood through your body. Your heart has four chambers. The atria are the two upper chambers in your heart—the right atrium and the left atrium. The ventricles... read more , a valve can become leaky and let blood flow backward in the heart
You can have an abnormal heart rhythm Overview of Abnormal Heart Rhythms Your heart is a muscle that pumps blood through your body. Your heart rate is how fast your heart beats. Your heart should always have a regular, rhythmic beat, like the ticking of a clock.... read more because of a problem with your heart's pacemaker or conduction system
Your heart's arteries can become blocked, called coronary artery disease Overview of Coronary Artery Disease (CAD) The heart is a muscle that pumps blood. Like all muscles, the heart needs a steady supply of blood to work. Blood that pumps through the heart doesn't feed the heart muscle. Instead the heart... read more , which can lead to a heart attack Heart Attack A heart attack is when blood flow to part of your heart is suddenly blocked and some of your heart muscle dies. Doctors use the term myocardial infarction to refer to a heart attack. Myocardium... read more