The heart is a pump. Its single most important job is to push blood through your entire body, delivering oxygen and nutrients to every cell and carrying waste products away. It does this continuously, beating roughly 100,000 times a day, moving about 5 liters (8 pints) of blood per minute through a vast network of blood vessels. Over a 70-year lifetime, that adds up to more than 2.5 billion beats.
How Blood Moves Through the Heart
Your heart has four chambers: two on the right side and two on the left. Each side has an upper chamber (atrium) that receives blood and a lower chamber (ventricle) that pumps it out. The right and left sides handle two different jobs, and blood flows through them in a specific sequence.
Oxygen-poor blood returning from your body enters the right atrium through two large veins. From there it moves into the right ventricle, which pumps it to your lungs. In the lungs, the blood picks up fresh oxygen and drops off carbon dioxide. That newly oxygenated blood then flows into the left atrium, passes into the left ventricle, and gets pumped out to the rest of your body through the aorta, the largest artery you have.
The left ventricle is the strongest chamber because it has to generate enough pressure to push blood all the way to your fingers, toes, and brain. Valves between each chamber act like one-way doors, opening to let blood through and snapping shut to prevent it from flowing backward. When a doctor listens to your heartbeat, the sounds they hear are those valves closing.
What Controls the Heartbeat
Your heart doesn’t wait for instructions from your brain to beat. It has its own built-in electrical system. A small cluster of cells called the SA node, located in the right atrium, fires an electrical signal that triggers each heartbeat. This is your heart’s natural pacemaker.
After the SA node fires, the signal travels through the upper chambers, causing them to contract and push blood into the lower chambers. The signal then reaches a second relay point, the AV node, near the center of the heart. The AV node deliberately delays the signal by a fraction of a second, giving the upper chambers enough time to empty completely before the lower chambers contract. This precise timing is what makes each heartbeat efficient.
How Your Heart Speeds Up and Slows Down
While the SA node sets the rhythm, your nervous system controls the tempo. Two branches of your autonomic nervous system, the part that runs on autopilot, constantly tug your heart rate in opposite directions.
Your sympathetic nervous system (the “fight or flight” branch) speeds the SA node up. When you exercise, feel stressed, or sense danger, this system releases signals that make your heart beat faster and harder so more blood reaches your muscles and brain. Your parasympathetic nervous system (the “rest and digest” branch) does the opposite, slowing the SA node down when you’re relaxed or sleeping. Your resting heart rate at any given moment reflects the balance between these two forces.
Normal Resting Heart Rate by Age
Heart rate varies significantly depending on how old you are. Newborns have the fastest resting rates, and the number gradually decreases into adulthood:
- Newborn (birth to 4 weeks): 100 to 205 bpm
- Infant (4 weeks to 1 year): 100 to 180 bpm
- Toddler (1 to 3 years): 98 to 140 bpm
- Preschool (3 to 5 years): 80 to 120 bpm
- School age (5 to 12 years): 75 to 118 bpm
- Adolescent (13 to 17 years): 60 to 100 bpm
- Adult (18 and older): 60 to 100 bpm
These ranges apply when you’re awake and not exercising. Your heart rate drops during sleep and climbs during physical activity. Well-trained athletes often have resting rates below 60 bpm because their hearts pump more blood per beat.
How Much Blood the Heart Pumps
At rest, a healthy adult heart pushes out 5 to 6 liters of blood per minute. That figure, called cardiac output, is the total volume of blood your heart delivers to your body in 60 seconds. It equals the amount of blood ejected with each beat (stroke volume) multiplied by the number of beats per minute.
During intense exercise, cardiac output can increase four to five times over the resting level. Your heart accomplishes this by beating faster and by squeezing out more blood with each contraction. This flexibility is what allows you to go from sitting on a couch to sprinting for a bus without passing out.
The Heart as a Hormone-Producing Organ
Pumping blood is the heart’s headline job, but it also functions as a hormone-producing organ. When the walls of the upper chambers stretch, typically because blood volume or blood pressure is too high, the heart releases hormones called natriuretic peptides into the bloodstream.
These hormones act on the kidneys, blood vessels, and adrenal glands in a coordinated way. They signal the kidneys to excrete more sodium and water, which reduces blood volume. They relax blood vessel walls, which lowers blood pressure. In effect, the heart monitors its own workload and sends chemical messages to other organs to lighten the load. This creates a feedback loop between the heart and kidneys that helps keep blood pressure and fluid balance in check.
What Happens When the Heart Can’t Keep Up
Because every organ depends on the heart for oxygen and fuel, problems with the heart ripple outward quickly. If the heart muscle weakens and can’t pump enough blood (heart failure), fluid can back up into the lungs, causing shortness of breath, or pool in the legs, causing swelling. If the electrical system misfires, the heart may beat too fast, too slow, or irregularly, reducing how efficiently it pumps.
Blocked arteries that feed the heart muscle itself can starve sections of tissue, leading to a heart attack. The heart muscle doesn’t regenerate well, so damaged areas are replaced with scar tissue that can’t contract. This is why prevention matters so much: the heart runs 24 hours a day with no breaks, and once it loses capacity, recovering that lost function is difficult.
Keeping the heart healthy comes down to the basics that support its enormous daily workload. Regular physical activity strengthens the heart muscle, improves its efficiency per beat, and lowers resting heart rate over time. Managing blood pressure, maintaining a healthy weight, and avoiding smoking all reduce the strain on a pump that will beat billions of times over a lifetime.