Final answer:
The two thick, muscular cavities in the heart that pump blood are called the ventricles.
Step-by-step explanation:
The two thick, muscular cavities in the heart that pump blood are called the ventricles. The heart has four chambers: two atria and two ventricles. The ventricles are responsible for pumping oxygenated blood to the body and deoxygenated blood to the lungs.