Which type of blood vessel carries blood back to the heart?

Veins are the type of blood vessels that are primarily responsible for returning blood to the heart. They carry deoxygenated blood from the body's tissues back to the heart, where it can then be pumped to the lungs for oxygenation. The structure of veins is adapted to this function; they have thinner walls compared to arteries and contain valves that prevent the backflow of blood, ensuring it moves efficiently toward the heart.

In contrast, arteries carry blood away from the heart and generally transport oxygenated blood, except for the pulmonary arteries, which carry deoxygenated blood from the heart to the lungs. Capillaries are the smallest blood vessels and are sites of gas and nutrient exchange between the blood and tissues. The aorta is the largest artery in the body, which conveys oxygenated blood from the heart to the rest of the body, but it does not have a role in carrying blood back to the heart. This distinction underscores the specific, crucial role that veins play in the circulatory system.