What is the pathophysiology of chest pain?

Depends on the cause. Chest pain can be a symptom of heart disease but may be may other things such as esophageal spasms, great vessel disease, respiratory disorders (asthma, COPD, bronchitis, infections), and muscle problems to name a few. It really depends on the clinical situation and other symptoms you may be having.
Several. Look at the cartoon for some causes of chest pain. See your doctor for evaluation.
Coronary occlusions. There are multiple causes of chest pain, the most common and ominous being coronary artery occlusions with atherosclerosis.