Let us start with where the heart is and what is around it. The heart is an organ about the size of your fist, and it pumps blood through your body. It sits in your chest between your lungs, a little to the left of the middle. The heart is made of muscle. The pericardium is a sac that surrounds the heart, holds it in place and protects it. Put a hand on your chest and you are close to all of this.

Now let us follow the signal, step by step. Each heartbeat starts with an electrical signal from the sinoatrial (SA) node in the right atrium. The SA node is the heart's pacemaker and sets the rate of the heartbeat. The electrical signal first makes the atria contract and push blood into the ventricles. The atrioventricular (AV) node carries the signal from the upper chambers to the lower chambers. The signal travels down the Purkinje fibers and makes the ventricles contract. That is the order the signal follows, one step after another.

Next comes the part of the heartbeat that has a sound. Between beats, the heart relaxes and its ventricles fill with blood. The ventricles are the two lower chambers of the heart, and they pump blood out of the heart. Valves inside the heart keep blood moving in the right direction. A heartbeat makes a "lub-DUB" sound. The "lub" sound is made by the valves between the atria and ventricles closing. With each heartbeat, the heart sends blood throughout your body.

Now follow the blood out to the body and back again. The left ventricle pumps oxygen-rich blood to the whole body, and the blood carries oxygen to every cell in your body. After the blood delivers oxygen, it returns to the heart, and the heart sends it to the lungs. The pulmonary artery carries oxygen-poor blood from the heart to the lungs, while oxygen-rich blood returns from the lungs to the heart through the pulmonary veins. That is the whole trip.

Now let us think about how fast the heart beats, and what the numbers mean. Your nervous system helps control your heart rate. Your pulse is the rate your heart beats, also called your heart rate. You can feel your pulse on the inside of your wrist, and to find your heart rate, you count the beats you feel in 30 seconds and double the number. At rest, a heart rate of 60 to 100 beats per minute is normal for adults. Your heart pumps more or less blood depending on what your body needs.

Last, think about how to look after your heart. Here are the facts that matter most. When you exercise, your heart beats faster to get more oxygen to your muscles. Aerobic exercises such as walking, running or swimming raise your heart rate and keep your heart, lungs and circulatory system healthy. Running, biking and swimming are exercises that are good for your heart, and as of November 2026, adults are advised to get at least 150 minutes of moderate-intensity aerobic activity a week.

Words to know

• pericardium: heart sac
• pacemaker: beat starter
• Purkinje: fiber name
• aerobic: heart-raising
• ventricles: lower chambers