The most common disorder in which heart pain occurs at night is unstable angina. The nature of chest discomfort in patients with unstable angina is similar to typical stable angina, usually of greater severity and longer duration, up to several 10 minutes, and chest pain can occur at rest. The pathology of patients with unstable angina is characterized by platelet aggregation on the basis of ruptured or eroded unstable atherosclerotic plaques, complicated by thrombosis, spastic constriction of coronary arteries, and microvascular embolism leading to acute or subacute lack of myocardial oxygen supply or increased ischemia. On clinical examination, the elevation of the ST segment of the electrocardiogram during the attack and the pseudo-normalization of the ST segment after the attack can be detected, and coronary angiography can be performed to further clarify the condition, which requires active treatment to avoid myocardial infarction.