Blood Flow Through the Heart and Lungs

How blood picks up oxygen to distribute throughout the body

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Blood flow through the heart and to the rest of the body involves four chambers, four valves, and many blood vessels. These work together to ensure a consistent supply of oxygenated blood gets where it needs to go.

Blood flow through the heart follows a lifelong rhythm in healthy people, though it may change due to other factors including daily activity, an underlying disorder, or a developing heart disease.

This article explains blood flow through the heart, step by step. It also discusses how this complex process might change during exercise or times of stress, as well as some of the causes of serious and life-threatening health effects when it's disrupted.

An illustration of the cardiovascular system
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Blood Flow: Step by Step

The heart has two upper chambers—the left and right atriums—and two larger lower chambers, the left and right ventricles. Four valves act like doorways, in a sequence used to control blood flow in and out of these chambers.

The cardiac conduction system sends out electric impulses to make the heart muscle contract and relax. Those pulses set the rate and rhythm of your heartbeat.

Here is what happens as blood flows through the heart and lungs:

  1. The blood first enters the right atrium.
  2. The blood then flows through the tricuspid valve into the right ventricle.
  3. When the heart beats, the ventricle pushes blood through the pulmonic valve into the pulmonary artery.
  4. The pulmonary artery carries blood to the lungs where it “picks up” oxygen.
  5. It then leaves the lungs to return to the heart through the pulmonary vein.
  6. The blood enters the left atrium.
  7. It drops through the mitral valve into the left ventricle.
  8. The left ventricle then pumps blood through the aortic valve and into the aorta. The aorta is the artery that feeds the rest of the body through a system of blood vessels.
  9. Blood returns to the heart from the body via two large blood vessels called the superior vena cava and the inferior vena cava. This blood carries little oxygen, as it is returning from the body where oxygen was used.
  10. The vena cavas pump blood into the right atrium and the cycle begins all over again.

Arteries generally transport oxygen-rich blood. The pulmonary artery is unique. It is the only artery in the body that carries oxygen-poor blood.

Importance of Valves

Without valves, the ventricles of the heart couldn’t build up any force or pressure. It would be like pumping up a flat tire with a huge hole in it. No matter how much effort you put into pumping, the tire would never inflate.

In the case of the heart, blood would come into the chamber and just slosh through it. It would exit the valve at the bottom, or upward in the wrong direction each time the ventricle tried to pump blood.

All four of the heart valves open and close at just the right times to keep the blood flowing through the heart in the right direction. Part of the sound of your heartbeat is valves closing.

Blood Flow Changes

A healthy heart normally beats anywhere from 60 to 70 times per minute when you're at rest. This rate can be higher or lower depending on your health and physical fitness. Athletes generally have a lower resting heart rate, for example.

Your heart rate rises when you move. That's because your muscles use oxygen while they work. The heart works harder to bring oxygenated blood where it is needed.

Disrupted or irregular heartbeats can affect blood flow through the heart. This can happen in many ways:

  • Electrical pulses are impacted, causing an arrhythmia, or irregular heartbeat. Atrial fibrillation is a common form of this.
  • Conduction disorders, or heart blocks, affect the cardiac conduction system. That's what regulates how electrical impulses move through the heart. The type of block—an atrioventricular (AV) block or bundle branch block—depends on where it is in the conduction system.
  • Damaged or diseased valves can stop working well or leak blood in the wrong direction.
  • A blocked blood vessel can disrupt blood flow gradually or suddenly. One example is a heart attack.

When to Worry About Blood Flow

If you have a sudden irregular heartbeat, or cardiac symptoms like chest pain and shortness of breath, call 911 for immediate medical help. Be sure to tell your healthcare provider about more chronic symptoms, like chest pain with exertion or swelling in your legs, that may indicate problems with blood flow.


Blood flow is a cycle that involves your lungs, heart chambers, valves, and blood vessels. Electrical pulses make your heart muscles squeeze and release. That action pushes blood through the two chambers on the right side of your heart and out to the lungs where it gathers oxygen.

A vein then carries that oxygen-rich blood into the left side of the heart. The two chambers on the left thrust the blood into arteries that carry blood and oxygen to the whole body.

When any part of that complex system breaks down, your body suffers from the lack of oxygen. Arrhythmia, valve disorders, and blockages in your heart or blood vessels can cause serious health problems. They may come on gradually or suddenly.

A Word From Verywell

Healthy blood flow is critical to overall health. Physical activity is one of the best ways to make sure your heart and lungs can function well over time. If you have health issues, ask your healthcare provider about how to keep your heart rate and rhythm—and your blood flow—healthy.

Frequently Asked Questions

  • In what direction does blood flow through the heart?

    De-oxygenated blood enters the right side of the heart and is pumped toward the lungs to pick up oxygen. Then that oxygen-rich blood re-enters the heart on the left side and is pumped out to the cells of the body.

  • Does exercise improve blood flow?

    Yes. Exercise strengthens your heart muscle and makes it more efficient, improving blood flow. It also reduces your risk of artery-clogging cholesterol and improves blood vessel function, among other things.

  • What affects your heart rate?

    Exercise and movement force your heart to beat faster and raise your heart rate. Many factors can also affect your resting heart rate, including medication, fitness level, body position, emotions, body mass, and even air temperature.

5 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. National Heart, Lung, and Blood Institute. Conduction Disorders.

  2. Centers for Disease Control and Prevention. How the Heart Works.

  3. National Heart, Lung, and Blood Institute. How the Heart Works.

  4. Pinckard K, Baskin KK, Stanford KI. Effects of exercise to improve cardiovascular health. Front Cardiovasc Med. 2019;6:69. doi:10.3389/fcvm.2019.00069

  5. American Heart Association. All About Heart Rate (Pulse).

Additional Reading

By Jennifer Whitlock, RN, MSN, FN
Jennifer Whitlock, RN, MSN, FNP-C, is a board-certified family nurse practitioner. She has experience in primary care and hospital medicine.