How does blood travel from the heart to lungs?

The heart's right atrium receives deoxygenated blood from the body tissues via superior vena cava and inferior vena cava. From the atrium, the blood is directed to the right ventricle. The right ventricle then pumps the deoxygenated blood to the lungs through the pulmonary artery.

The pulmonary artery transports deoxygenated blood from the right ventricle to the capillaries that surround the alveoli. In the alveoli, blood is oxygenated through a process called diffusion, where carbon dioxide is released from the blood, while oxygen is absorbed into the blood.

Hence, the deoxygenated blood that left the heart is now oxygenated and returns to the heart through pulmonary veins. The oxygenated blood enters the left atrium and is then directed to the left ventricle, which pumps it out to the rest of the body via the aorta.