CARDIAC MUSCLES -

1. The cardiac muscles are found in the wall of the heart and in the wall of large veins (e.g., pulmonary veins and superior vena cava) where these veins enter the heart.
2. These fibres show the characters of both unstriped and striped muscle fibres. Each fibre is a long and cylindrical structure which lacks a definite sarcolemma.
3. The fibres are uninucleate and the nuclei lie near the centre.
4. The fibres have some lateral branches, known as oblique bridges to form a contractile network.
5. The myofibrils have transverse faint dark and light bands, which alternate with each other. In this way cardiac muscle fibres are also striped, but having dark intercalated discs at intervals.
6. The intercalated discs are specialized regions of cell membrane of two adjacent fibres. The intercalated discs function as boosters of contraction wave and permit the wave of muscle contraction to be transmitted from one cardiac fibre to another.

UNIQUE FEATURES -

1. Cardiac muscle fibres are supplied with both central and autonomic nervous system and are not under the control of the will of the animal.
2. However, these muscles never get fatigued. Thus they are immune to fatigue.
3. Blood capillaries penetrate the cardiac muscle fibres.
4. They have very rich blood supply.
5. They have the property of contraction, even when they are isolated from the body temporarily.