Blood from the right ventricle goes to the lungs. When the right ventricle contracts, it pushes oxygen-poor blood through the pulmonary valve and into the pulmonary artery, which carries it to the left and right lungs. There, the blood picks up fresh oxygen and releases carbon dioxide before returning to the heart’s left side for delivery to the rest of the body.
The Path From Right Ventricle to Lungs
The right ventricle sits in the lower right portion of your heart and serves one purpose: pumping blood to your lungs. The sequence is straightforward. When the right ventricle contracts, the pulmonary valve opens, and blood flows into the pulmonary trunk (the main pulmonary artery). That trunk quickly splits into the left and right pulmonary arteries, each heading to the corresponding lung.
The pulmonary valve acts as a one-way door between the right ventricle and the pulmonary artery. It has three small flaps, called leaflets, that snap open during each heartbeat to let blood through, then close tightly when the heart relaxes to prevent blood from leaking backward. This open-close cycle happens with every single beat, roughly 100,000 times a day.
The pressure driving this flow is relatively low. The right ventricle generates a systolic pressure of about 17 to 32 mmHg, far less than the left ventricle, which pumps blood to the entire body at pressures around 120 mmHg. The lungs don’t need high pressure because they sit right next to the heart and have a delicate network of tiny blood vessels that could be damaged by forceful flow. The right ventricle’s wall reflects this lighter workload: it’s noticeably thinner than the muscular left ventricle.
What Happens Inside the Lungs
Once blood reaches the lungs through the pulmonary arteries, those arteries branch into smaller and smaller vessels until they become capillaries, microscopic blood vessels woven into the walls of the alveoli (tiny air sacs in the lungs). This is where gas exchange takes place.
Oxygen from inhaled air passes through the thin walls of the alveoli and into the surrounding capillaries, attaching to red blood cells. At the same time, carbon dioxide, a waste product your cells have been dumping into the blood, moves in the opposite direction, crossing from the capillaries into the alveoli. You then exhale that carbon dioxide. The blood entering this exchange carries an oxygen saturation of roughly 71%, meaning most of its oxygen has already been used by the body. By the time it leaves the lungs, saturation climbs to 95% or higher.
Completing the Circuit
After picking up oxygen, the now oxygen-rich blood exits the lungs through the pulmonary veins, four in total, and flows into the left atrium of the heart. From there it passes into the left ventricle, which pumps it out through the aorta to supply oxygen to every tissue in the body. Once tissues extract the oxygen they need, the blood returns through veins to the right atrium, drops into the right ventricle, and the cycle starts again.
This loop from the right ventricle through the lungs and back to the left atrium is called pulmonary circulation. It runs in parallel with systemic circulation, the loop that delivers blood from the left ventricle to your organs and back. Both circuits operate simultaneously with every heartbeat.
How Fetal Circulation Differs
Before birth, the right ventricle’s blood takes a very different route. A fetus doesn’t breathe air, so sending large volumes of blood to the lungs would be pointless. Instead, most blood pumped from the fetal right ventricle bypasses the lungs entirely. It flows from the pulmonary artery through a short vessel called the ductus arteriosus directly into the aorta, mixing with blood headed for the body. The fetus gets its oxygen from the placenta, not from its own lungs.
At birth, a newborn’s first breath drops the resistance in the lung blood vessels dramatically. Blood begins flowing through the lungs for the first time, and the ductus arteriosus gradually closes over the following hours to days. From that point on, the right ventricle’s entire output goes to the lungs, just as it does for the rest of life.
When This Pathway Gets Disrupted
Several conditions can interfere with blood flow from the right ventricle to the lungs. Pulmonary hypertension, abnormally high pressure in the lung’s blood vessels, forces the right ventricle to work much harder than it was designed for. Over time, this extra strain can cause the right ventricle to weaken and fail, a condition called right heart failure.
A pulmonary embolism (a blood clot lodged in a pulmonary artery) creates a sudden blockage that can spike pressure in the right ventricle within minutes. Chronic lung diseases like severe pneumonia or acute respiratory distress syndrome also raise pulmonary pressure and stress the right side of the heart. Congenital heart defects, such as a narrowed pulmonary valve (pulmonic stenosis) or structural problems like tetralogy of Fallot, can obstruct right ventricular outflow from birth and often require surgical correction.
Problems with the pulmonary valve itself are another source of trouble. If the valve doesn’t close completely, blood leaks backward into the right ventricle (regurgitation), forcing it to handle extra volume with each beat. If the valve is too narrow, the ventricle has to generate higher pressure to push blood through, thickening its walls over time in a way that eventually compromises its pumping ability.