The structural and functional unit of the heart is the cardiac muscle cell, also known as the cardiomyocyte. These are specialised muscle cells that form the heart muscle wall. Their main role is to contract and relax in a coordinated manner so the heart can pump blood efficiently to the lungs and the rest of the body. Cardiomyocytes are connected like a network, allowing electrical signals to pass quickly from one cell to another. This ensures the heart beats in a smooth and regular rhythm without delays or interruptions. The heartbeat is controlled by a natural pacemaker called the sinoatrial node, which sends signals that instruct these cells when to contract. When all these cells work together properly, the heart functions as a strong and efficient pump. However, if the cells are damaged due to disease or other conditions, the heart may become weaker and less effective in circulating blood.