Cardiac muscle
The cardiac muscle (also known as the myocardium) was an involuntary muscle that formed of the walls of the heart. 

Following the death of Acamarian Gatherer Volnoth in 2366, Doctor Beverly Crusher initially guessed cardiac arrest to be the cause of death, further diagnosing it as a heart attack, but remained unconvinced because she could not find a cause due to the fact that the cardiac muscle of the deceased was strong, with no sign of arterial occlusion. Further investigation revealed that Penthor-Mul had died under similar circumstances in 2313. Crusher later determined that the cause of these heart attacks were a microvirus in his body, designed to block the autonomic nerve impulses only of those specifically from the Lornak clan. ()

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Anatomy