I woke up this morning with chest pain has been quite mild throughout the day, except when I stretch backwards or side to side. Could it be a heart attack or just a muscle pain?

Chest pain that is aggravated by stretching, changes in body position, or compression of the chest wall rarely are due to heart disease. Rather, inflammation or injury of the chest wall (eg costochondritis) is the most likely cause of such pain. Sleeping in an unusual position is a way to trigger pain in the chest wall. Cardiac chest pain tends to worsen with exertion and usually decreases or disappears with rest. Furthermore, non-cardiac chest pain is often associated with other symptoms such as sweating, nausea, palpitations, dizziness and shortness of breath. That said, if you have any risk factors for heart disease, persistent or recurrent chest pain should see their doctor.