Is the heart muscle affected by ALS?

In ALS, voluntary motor function—which is controlled by motor neurons in the brain and spinal cord—is affected. The heart muscle is not part of the voluntary motor system and is therefore not affected by the degeneration of motor neurons.

Although the heart muscle is spared, heart function may still be affected. Heart rhythm is regulated by the autonomic nervous system (also known as the vegetative nervous system). In a small number of ALS patients, the autonomic nervous system is affected, leading to associated heart rhythm disturbances. 5–10% of ALS patients die quite suddenly and without any apparent cause related to malnutrition or respiratory dysfunction. This cause of sudden and unexpected death is very likely due to involvement of the autonomic nervous system and the development of cardiac arrhythmias. Cardiac arrhythmias have been repeatedly reported in patients on long-term mechanical ventilation (and thus with a very long duration of illness).

Overall, however, ALS is a neurological disorder in which the heart muscle remains completely intact, and cardiac dysfunction may occur in a small group of patients, usually after a prolonged course of the disease.