Cardiac muscle Coloured transmission electron micrograph TEM of cardiac muscle fibrils brownfrom a healthy heart Mitochondria yellow supply the muscle cells with energy The muscle fibrils or myofibrils are crossed by transverse tubules dark brown lines These tubules mark the division of the myofibrilsinto contractile units sarcomeres Cardiac muscle is under subconscious control and continuously contracts to pump blood around the body without tiring Magnification x when printed centimetres across
