The right side of the heart pumps blood to the lungs. Specifically, the right ventricle does the heavy lifting, contracting with each heartbeat to push oxygen-poor blood into the pulmonary artery and onward to the lung tissue, where it picks up fresh oxygen and releases carbon dioxide. The left side, by contrast, receives that newly oxygenated blood and sends it out to the rest of the body.
How Blood Moves Through the Right Side
Blood returning from your body enters the heart through two large veins that empty into the right atrium, the upper chamber on the right side. This blood has already delivered most of its oxygen to your tissues. Oxygen saturation in the right side of the heart typically runs between 64% and 88%, compared to roughly 95% to 99% in arteries carrying blood away from the left side.
From the right atrium, blood passes through a one-way valve into the right ventricle, the lower chamber. When the right ventricle contracts, a second valve called the pulmonary valve opens, letting blood flow into the pulmonary artery and toward the lungs. The pulmonary valve has three small flaps that snap shut between beats, preventing blood from leaking backward into the ventricle. The entire trip from the right ventricle through the lungs and back to the left side of the heart takes about 6 seconds at a normal resting heart rate.
Why the Right Side Is Built Differently
If you compared the two sides of the heart, the difference in muscle thickness is striking. The right ventricle wall averages about 9 millimeters thick, while the left ventricle is roughly three times thicker. That 1:3 ratio exists because each side faces a very different workload.
The right ventricle only needs to push blood through the lungs, a short, low-pressure circuit. Normal pressure in the pulmonary arteries averages around 20 mmHg or less. The left ventricle, on the other hand, must generate enough force to send blood through every organ and extremity in your body, a much longer route with far more resistance. So while both sides pump the same volume of blood per beat, the left side needs considerably more muscle to do its job.
What Happens in the Lungs
Once blood reaches the lungs, it flows through increasingly tiny vessels until it arrives at the alveoli, microscopic air sacs where gas exchange takes place. Carbon dioxide passes out of the blood and into the air you exhale, while oxygen from the air you inhale crosses into the blood. This is the entire reason the right side of the heart exists as a separate pump: to keep a steady stream of blood flowing past those air sacs so your body maintains a constant supply of oxygen.
The freshly oxygenated blood then travels through pulmonary veins back to the left atrium, completing the pulmonary circuit. From there, the left ventricle takes over and pumps it to the brain, muscles, organs, and every other tissue that needs it.
When the Right Side Struggles
Because the right ventricle is thinner and designed for low-pressure work, it can be vulnerable when conditions change. Pulmonary hypertension, which is abnormally high pressure in the lung’s blood vessels (above 20 mmHg on average), forces the right ventricle to work harder than it was built for. Over time, the muscle can weaken.
Right-sided heart failure develops when the right ventricle can no longer pump effectively. Common signs include swelling in the legs and ankles, fatigue, reduced exercise tolerance, and fluid buildup in the abdomen. These symptoms happen because blood backs up in the veins leading to the heart rather than moving forward into the lungs. Lung diseases, blood clots in the pulmonary arteries, and certain congenital heart defects can all place extra strain on the right side.
Left-sided heart failure is actually one of the most common causes of right-sided problems. When the left side weakens, pressure builds in the lungs, and the right ventricle has to push against that increased resistance with every beat. Eventually, both sides can fail together.
The Two-Pump System at a Glance
- Right atrium: Collects oxygen-poor blood returning from the body
- Right ventricle: Pumps that blood through the pulmonary valve into the pulmonary artery
- Lungs: Blood picks up oxygen and drops off carbon dioxide
- Left atrium: Receives oxygen-rich blood from the lungs
- Left ventricle: Pumps oxygenated blood out to the entire body
Your heart completes this full double loop with every single beat, roughly 100,000 times a day. The right side quietly handles the pulmonary half of that circuit, ensuring every red blood cell gets reloaded with oxygen before the left side sends it on its way.