From Biology-Online Dictionary | Biology-Online Dictionary


noun, plural: myocardia

The muscular substance of the heart located at the middle, in between the epicardium and the endocardium

adjective: myocardial

Of, characteristic, or pertaining to the myocardium


The heart of the vertebrates is a muscular organ that pumps the blood to various parts of the body. It moves the blood through rhythmic contractions. The wall of the heart is made up of three layers: (1) epicardium, (2) myocardium, and (3) endocardium. The epicardium is the outer layer whereas the endocardium is the innermost layer of the heart. The myocardium is the middle layer and is the muscular substance of the heart. The myocardium is also referred to as the cardiac muscle (heart muscle). The cardiac muscle is a type of muscle that contracts involuntarily. When viewed under a microscope, the cardiac muscle cells have striations but they are not fused together. They are joined through a junctional complex that is referred to as the intercalated disc. The cardiac muscle has autorhythmicity, i.e. the ability to initiate an action potential at a fixed rate and spread the impulse from cell to cell so as to trigger the contraction of the entire heart.

Word origin: Ancient Greek mûs (muscle) + kardía (heart)

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