How Blood Flows Through the Heart and Lungs

The cardiovascular system

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The heart is a complex organ, using four chambers, four valves, and multiple blood vessels to provide blood to the body. Blood flow itself is equally complex, involving a cyclic series of steps that move blood trough the heart and to the lungs to be oxygenated, deliver it throughout the body, then bring blood back to the heart to re-start the process.

This is the key function of the cardiovascular system: consuming, transporting, and using oxygen throughout physical activity (which includes when you are at rest). Disruptions in blood flow through the heart and lungs can have serious effects.

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. A series of valves control blood flow in and out of these chambers.

Electrical impulses, controlled by the cardiac conduction system, make the heart muscle contract and relax, creating the rate and rhythm of your heartbeat.

The blood first enters the right atrium. It then flows through the tricuspid valve into the right ventricle. When the heart beats, the ventricle pushes blood through the pulmonic valve into the pulmonic artery.

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

The pulmonic artery carries blood to the lungs where it “picks up” oxygen and then leaves the lungs to return to the heart through the pulmonic vein.

The blood enters the left atrium, then descends through the mitral valve into the left ventricle. The left ventricle then pumps blood through the aortic valve and into the aorta, the artery that feeds the rest of the body through a system of blood vessels.

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.

The vena cavas pump blood into the right atrium and the cycle of oxygenation and transport begins all over again.

Importance of Valves

Without valves, the ventricles of the heart couldn’t develop any force or pressure. It would be like pumping up a flat tire with a huge hole in it: No matter the 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, exiting out 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.

Positive and Negative Effects on Blood Flow

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 with physical activity, as your muscles consume 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 multiple ways:

  • Electrical impulses that regulate your heartbeat are impacted, causing an arrythmia, or irregular heartbeat. Atrial fibrillation is a common form of this.
  • Conduction disorders, or "heart blocks," affect the cardiac conduction system, which regulates how electrical impulses move through the heart. The type of block—an atrioventricular (AV) block or bundle branch block—depends on where it occurs in the conduction system.
  • Damaged or diseased valves can become ineffective or leak blood in the wrong direction.
  • A blocked blood vessel, which can happen gradually or suddenly, can disrupt blood flow, such as during a heart attack.

If you experience an irregular heartbeat or cardiac symptoms like chest pain and shortness of breath, seek medical help immediately.

A Word From Verywell

Healthy blood flow is critical to overall health. Physical activity is one of the best ways to achieve and maintain optimal functioning of your heart and lungs. If you have health issues, partner with your doctor on the best way to keep your heart rate and rhythm—and therefore, your blood flow—healthy. It's one of the most important things you can do for a long life.

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Article 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. Center for Disease Control and Prevention. How the heart works. Reviewed November 12, 2019.

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

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