1. Severe bradycardia Patients whose heart stops for more than 3 seconds or whose heart rate frequently falls below 40 beats, especially if they experience blackness in front of the eyes and sudden fainting, should have a pacemaker implanted. This is the main and initial therapeutic category of pacemakers. 2. Weakness of heart contraction Diseases that destroy the heart muscle or change its original form can lead to the inability of the heart muscle to contract forcefully. A decrease in heart contraction will cause the heart to under-pump and prevent all parts of the body from receiving sufficient fresh blood, resulting in various symptoms such as dizziness, chest tightness, and weakness. In cases of congestive heart failure and severe hypertrophic obstructive cardiomyopathy where drug therapy is ineffective, multiple pacemakers can be installed in various parts of the heart to synchronize multiple electrical stimulation commands to help the heart muscle contract. Cardiac arrest can be fatal if the heart stops beating for a few minutes. Some diseases can trigger cardiac arrest or fatal malignant ventricular arrhythmias (e.g., rapid ventricular tachycardia, ventricular fibrillation), and pacemakers with defibrillator function can be installed, which can restore the regular beating of the heart. Pacemakers are also indispensable or the only treatment in certain cardiac complexes (carotid sinus hypersensitivity syndrome, vasovagal syncope, idiopathic Q-T prolongation syndrome, prevention of rapid atrial arrhythmias, etc.).