Final answer:
Chest pain not relieved by rest and nitroglycerin may indicate a myocardial infarction, which requires immediate medical care.
Step-by-step explanation:
Chest pain that is not relieved by rest and nitroglycerin may signal a myocardial infarction (MI), also known as a heart attack. While angina can present with similar symptoms, it is typically relieved with rest and nitroglycerin. A myocardial infarction indicates that the heart muscle is experiencing prolonged lack of oxygen, often due to a blocked coronary artery, which requires immediate medical attention. Unstable angina, which may occur at rest and is not relieved by nitroglycerin, could precede a myocardial infarction and is also considered a medical emergency.