Not really answering the question
How the heart works is covered in GCSE biology. Physical differences from a mechanical pump are only half the story.
The heart really differs from other mechanical pumps, in a functional sense, in that the pressure remains very low throughout, and this prevents the blood cells from being destroyed (haemolysis). This is one of the major barriers to replacing the heart with a mechanical alternative.
Pumps which do mimic the low pressure conditions tend to be too large to implant in a patient.