Which chamber of the heart is regarded as the hardest working?

The left ventricle is regarded as the hardest working chamber of the heart because it is responsible for pumping oxygenated blood to the entire body. Unlike the other chambers, which either receive blood or pump it to the lungs for oxygenation, the left ventricle must generate significant pressure to ensure that blood circulates effectively through the systemic circulation. This requires strong muscular walls to enable powerful contractions during systole, the phase of the heartbeat when the heart contracts.

In contrast, the right atrium and right ventricle deal with deoxygenated blood returning from the body and sending it to the lungs for oxygenation, which requires less force compared to the high pressure needed to push blood throughout the body from the left ventricle. The left atrium receives blood from the lungs and also does not need to exert as much force as the left ventricle. Therefore, the left ventricle's role and the demands placed upon it highlight its status as the hardest working chamber of the heart.