Question

In a coloured diagram, why do we generally show the pulmonary artery in blue and pulmonary vein in red colour?

Answer 1

1. The pulmonary artery, which transports deoxygenated blood from the heart to the lungs, is usually represented in blue. 
2. The pulmonary vein, which transports oxygenated blood from the lungs to the heart, is usually represented in red.