Heart muscle. Confocal light micrograph of a section through cardiac (heart) muscle. Cardiac muscle consists of branching elongated muscle cells, called myocytes (stained with green fluorescent protein), which form fibres. Myocytes consist of microfilaments of the contractile proteins actin and myosin, and a centrally located nucleus (blue). Calcium-binding protein is stained red. Calcium is essential for signalling between the nerves and muscle fibres, and for the contraction of the muscle fibres. Cardiac muscle is myogenic, it can cause its own contraction without any other input. A blood vessel (oval) is seen at centre left.