# Double circulation

Mammals pump blood through two loops. The right side sends blood to the lungs to pick up oxygen. The left side sends oxygen-rich blood to the body. The heart has four chambers to keep the two kinds of blood apart.

Biology (university) · Part 09: Animal physiology · Card 5 of 9 · Last updated 2026-10-19

## Analogy

Two separate delivery routes with a pump in the middle.

## In practice

The left ventricle has the thickest wall because it must push blood around the whole body.

## Practice

### Flashcards

- **Why is the left ventricle thicker than the right?** It pumps blood around the whole body, which needs more pressure than the lungs.

## Questions people ask

### Why do mammals need a double circulation?

Blood passing through the lungs loses pressure. If it then went straight on to the body, flow would be slow. A second pump boosts the pressure again, giving fast delivery of oxygen to tissues. This supports the high energy use of warm-blooded animals.

### What does a heartbeat consist of?

A heartbeat has a filling and a pumping part. The atria contract first and push blood into the ventricles. The ventricles then contract, sending blood into the arteries. Valves close behind it, which creates the familiar lub-dub sound and prevents backflow.

## Related concepts

- [Oxygen transport](https://studyvisually.com/learn/science/biology-university/biology-university-part-9/biology-university-part-9-concept-6)

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