Cardiac muscle works much harder and longer without tiring than other muscles do. It can do that because it has a larger number of than other muscle cells.

Cardiac muscle needs a steady supply of energy to keep contracting continuously. Mitochondria produce much of the energy muscle cells use, so cardiac muscle cells have many mitochondria. Fascicles are bundles of muscle fibers, and tissues are groups of cells; neither explains the muscle’s endurance.

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