Blood flows twice in the heart before it complete one full round: 1. Pulmonary circulation and 2. Systemic circulation. So blood circulation is called as double circulation.

1. Pulmonary circulation: It is the shortest circulation. Pulmonary artery takes blood from right ventricle to lungs, and after oxygenation of the blood in the lungs, pulmonary veins carry blood from lungs to left auricle of the heart.

2. Systemic circulation: It is long circulation. Aorta which divides further into arteries in the body carries blood from left ventricle to whole body and veins in the body collects the deoxygenated blood from whole body and pour back into the heart via venacava.

Note: both types of circulation take place simultaneously.

MEB3: Why blood circulation is also called as double circulation?

MEB3: Explain the types of circulation?

Image source:

https://images.topperlearning.com/topper/tinymce/imagemanager/files/769c203341ee71958573d806676448a55b2a5938238a10.37771893Doublecirculation2.png