How does a heart attack cause shooting pain down the left arm?

Left arm pain: Visceral pain is pain is carried afferent fibers (type of nerve) of the autonomic nervous system. The visceral nerves are designed to tell you that something is wrong but not exactly where. The nerves of the heart and left jaw, shoulder, and arm overlap. There is individual variation in the spinal cord distribution. Pain from a heart attack may occur in any or all of those areas.

Classically: Angina pectoris =substernal pressure, pain with radiation to the neck or left or right arm and shoulder. Some will have abdominal pain-and be confused with gallbladder or stomach symptoms. Ladies seem to have less classic// or tolerate pain better than men. Relief with Nitroglycerin is very suggestive. A feeling of impending doom, pallor, sweating suggest a bad day!