A normal heart is a fist-sized muscular organ that pumps blood through your entire body using four chambers, four valves, and a built-in electrical system that keeps everything firing in rhythm. In a healthy adult, it beats 60 to 100 times per minute at rest, pushes out about 5 to 6 liters of blood every minute, and maintains a blood pressure below 120/80 mmHg. Understanding what “normal” looks like across all these measures gives you a baseline for recognizing when something is off.
Size, Weight, and Basic Structure
The adult heart sits slightly left of center in your chest, roughly the size of your clenched fist. A healthy male heart weighs around 374 grams on average (about 13 ounces), while a female heart averages about 285 grams (10 ounces). Hearts above 500 grams in men or 400 grams in women are considered abnormally enlarged, which can signal conditions like chronic high blood pressure or valve disease.
Inside, the heart has four chambers. The two upper chambers, called atria, receive incoming blood. The two lower chambers, called ventricles, pump blood out. The right side of the heart handles oxygen-poor blood returning from the body, sending it to the lungs to pick up fresh oxygen. The left side receives that oxygen-rich blood from the lungs and pumps it out to the rest of the body through the aorta, your largest artery. The left ventricle is the strongest chamber because it needs to generate enough pressure to push blood all the way to your fingers and toes.
How Blood Flows Through a Healthy Heart
Blood follows a one-way loop. Oxygen-depleted blood enters the right atrium through two large veins, then moves into the right ventricle, which pumps it to the lungs through the pulmonary artery. In the lungs, the blood drops off carbon dioxide and picks up oxygen. It then returns to the heart through the pulmonary veins, entering the left atrium. From there it flows into the left ventricle, which pumps it out through the aorta to supply every organ and tissue in your body.
Four valves keep blood moving in the right direction and prevent backflow. The tricuspid valve sits between the right atrium and right ventricle. The pulmonary valve guards the exit from the right ventricle to the lungs. On the left side, the mitral valve separates the left atrium and left ventricle, and the aortic valve controls the exit into the aorta. When these valves open and close properly, they create the familiar “lub-dub” heartbeat sound.
What Creates the Heartbeat Sound
The first sound, the “lub,” happens when the mitral and tricuspid valves snap shut as the ventricles begin to contract. The second sound, the “dub,” occurs when the aortic and pulmonary valves close after the ventricles finish pumping. These two sounds, called S1 and S2 in medical shorthand, are what a doctor listens for with a stethoscope. In a normal heart, they have a steady, predictable rhythm with no extra whooshing or clicking sounds between them.
There’s a subtle detail even within the second sound. The aortic valve typically closes a fraction of a second before the pulmonary valve, and this tiny gap widens slightly when you breathe in. That slight split is completely normal and happens because your lungs pull in more blood during inhalation, giving the right ventricle a bit more work to do.
Normal Resting Heart Rate by Age
Heart rate varies dramatically depending on age. Newborns have the fastest resting rates, between 100 and 205 beats per minute, because their small hearts need to beat more frequently to circulate enough blood. By school age (5 to 12 years), normal range drops to 75 to 118 bpm. Adolescents and adults share the same range: 60 to 100 bpm at rest.
If you’re physically active or an endurance athlete, a resting heart rate in the 40s or 50s is common and healthy. Regular exercise strengthens the heart muscle so it can pump more blood per beat, meaning it doesn’t need to beat as often. Your heart rate naturally rises during physical activity, stress, or caffeine intake, and drops during sleep. What matters most is where it sits consistently when you’re calm and awake.
How Much Blood the Heart Pumps
Each time the left ventricle contracts, it ejects a specific volume of blood called stroke volume. In healthy adults, this averages about 70 to 75 milliliters per beat in men and around 66 milliliters per beat in women. Multiply stroke volume by heart rate and you get cardiac output: the total amount of blood your heart pumps per minute. For a healthy person at rest, that works out to roughly 5 to 6 liters per minute, which is essentially your entire blood supply circulating through your body once every 60 seconds.
A related measure is ejection fraction, which tells you what percentage of blood in the left ventricle actually gets pumped out with each beat. A normal ejection fraction is 50% to 70%. That means if the ventricle fills with 120 milliliters of blood, it pushes out 60 to 84 milliliters and retains the rest. An ejection fraction below 50% suggests the heart isn’t pumping efficiently, which is one of the key markers doctors use to diagnose heart failure.
The Heart’s Electrical System
Your heartbeat isn’t triggered by your brain. The heart has its own electrical system with a built-in pacemaker called the sinus node, located in the right atrium. This node fires an electrical signal that spreads across both atria, causing them to contract and push blood into the ventricles. The signal then travels to the ventricles, triggering them to contract a split second later. This coordinated sequence, atria first, ventricles second, is what makes the heart an efficient pump.
When this system works correctly, doctors call it normal sinus rhythm. On an electrocardiogram (ECG), it shows up as a repeating pattern of waves. A small rounded wave (the P wave) represents the atria contracting, followed by a taller, sharper spike (the QRS complex) representing the ventricles contracting. In a normal reading, each heartbeat produces the same pattern at regular intervals, and the entire electrical signal travels through the heart in under a tenth of a second. Irregular patterns on an ECG can reveal problems like arrhythmias, where the heart beats too fast, too slow, or out of rhythm.
Normal Blood Pressure
Blood pressure measures the force of blood pushing against your artery walls, and it’s reported as two numbers. The top number (systolic) captures the pressure when the heart contracts. The bottom number (diastolic) captures the pressure when the heart relaxes between beats. According to the American Heart Association, normal blood pressure is below 120/80 mmHg.
Once your systolic reading consistently lands between 120 and 129 with a diastolic still under 80, you’ve moved into the “elevated” category. This isn’t hypertension yet, but it’s a signal that your blood pressure is trending upward. Blood pressure naturally fluctuates throughout the day, rising during exercise or stress and falling during rest, so a single high reading doesn’t necessarily mean there’s a problem. The pattern over time is what counts.
What Keeps a Heart “Normal”
A normal heart depends on several systems working together: strong, flexible heart muscle that contracts efficiently, valves that open and close completely without leaking, coronary arteries that deliver enough oxygen-rich blood to the heart muscle itself, and an electrical system that fires signals in the right order at the right pace. When any one of these components breaks down, whether through plaque buildup in arteries, valve deterioration, muscle thickening, or electrical misfiring, the heart compensates for a while but eventually shows signs of disease.
The numbers that define a normal heart aren’t fixed for every person. Body size, fitness level, age, and genetics all shift what’s healthy for you specifically. But the general benchmarks, a resting rate of 60 to 100 bpm, blood pressure under 120/80, an ejection fraction of 50% or higher, provide a useful framework for tracking your heart health over time.