The heart is a muscle about the size of your fist. It works like a pump and beats 100,000 times a day.
The heart has two sides, separated by an inner wall called the septum. The right side of the heart pumps blood to the lungs to pick up oxygen. The left side of the heart receives the oxygen-rich blood from the lungs and pumps it to the body.
The heart has four chambers and four valves and is connected to various blood vessels. Veins are blood vessels that carry blood from the body to the heart. Arteries are blood vessels that carry blood away from the heart to the body.
The heart has four chambers or "rooms."
Four valves control the flow of blood from the atria to the ventricles and from the ventricles into the two large arteries connected to the heart.
Valves are like doors that open and close. They open to allow blood to flow through to the next chamber or to one of the arteries. Then they shut to keep blood from flowing backward.
When the heart's valves open and close, they make a "lub-DUB" sound that a doctor can hear using a stethoscope.
The arteries are major blood vessels connected to your heart.
The veins also are major blood vessels connected to your heart.
For more information about how a healthy heart works, go to the Health Topics How the Heart Works article. This article contains animations that show how your heart pumps blood and how your heart's electrical system works.
Clinical trials are research studies that explore whether a medical strategy, treatment, or device is safe and effective for humans.
Interested in learning more about heart disease in women? View a Storify archive of a September 28, 2012, Twitter chat on women’s heart health. The discussion includes experts from The Heart Truth®, Million Hearts™, healthfinder.gov, and the American College of Cardiology’s CardioSmart™
The NHLBI updates Health Topics articles on a biennial cycle based on a thorough review of research findings and new literature. The articles also are updated as needed if important new research is published. The date on each Health Topics article reflects when the content was originally posted or last revised.