The heart of any computer is the CPU.

The CPU, or rather microprocessor, is the heart of any computer system. The microprocessor calculates, performs logical operations and manages data flows by reading instructions from memory and then executing them.

Assuming you mean that the CPU (central processing unit) is the brain of the computer system, the heart of the computer system would be the clock signal on the motherboard, which provides a regular beat that allows the CPU to proceed with its work.

The central processor unit (CPU), often called just the 'processor', is the heart of the PC. It controls everything that happens in the computer and it's overall performance is determined by a number of factors: