Chest pain is a common reason for emergency room visits. According to the document, chest pain accounts for over 2 million ER visits per year in the US. It can be difficult to accurately diagnose the underlying cause of chest pain. The document discusses several cases of patients presenting with chest pain and the process of gathering a history, performing a physical exam, ordering tests, and considering potential diagnoses for each case, including acute myocardial infarction, pericarditis, pulmonary embolism, and aortic dissection.