Blood begins its journey through the heart when it is returned to the right atrium from the body in need of oxygen. From the right atrium, the blood flows into the right ventricle, which serves as a pump that delivers the blood to the lungs. Within the lungs, the blood releases waste gases and acquires oxygen. This newly oxygen-rich blood returns from the lungs to the left atrium and flows into the left ventricle. Finally, the left ventricle pumps the oxygen-rich blood out of the heart to all parts of the body.
The human body has about 5.6 liters (6 quarts) of blood, all of which circulates through the body three times every minute.
References:
Medical Modeling: The Human Heart. asileFX.
MRI data.