Heart muscle. Confocal light micrograph of a section through cardiac (heart) muscle. Cardiac muscle consists of branching elongated muscle cells, called myocytes (red), which form fibres (running horizontally). Myocytes consist of microfilaments of the contractile proteins actin and myosin, and a centrally located nucleus (blue). The microfilaments are crossed by transverse tubules (vertical lines) that mark the division of the microfilaments into contractile units (sarcomeres). Cardiac muscle is myogenic, it can cause its own contraction without any other input.