Indication: 1. As secondary prevention, to reduce the mortality of myocardial infarction. 2. Hypertension (alone or in combination with other antihypertensive drugs). 3. Exertional angina pectoris. 4. Control supraventricular tachyarrhythmias and ventricular arrhythmias, especially arrhythmias related to catecholamines or caused by digitalis. It can be used to control the ventricular rate of atrial flutter and atrial fibrillation that are not well treated with digitalis, and can also be used for refractory premature contractions to improve patients' symptoms. 5. Reduce the outflow tract pressure gradient in hypertrophic cardiomyopathy, relieve symptoms such as angina pectoris, palpitations and syncope. 6. Used in combination with receptor blockers to control tachycardia in patients with pheochromocytoma. 7. Used to control the rapid heart rate of hyperthyroidism, and can also be used to treat thyroid crisis.