In the process of heart failure, about 30% of patients have heart enlargement and cardiac dysynchronization, which is manifested by left and right ventricular contraction asynchrony, left ventricular free wall and septal contraction asynchrony, and atrial and ventricular contraction asynchrony, resulting in reduced heart beat volume, mitral valve incomplete closure, and mitral regurgitation, which aggravate heart failure. This cardiac desynchronization phenomenon is not treated with medication. Cardiac resynchronization therapy involves the implantation of three electrodes in the right atrium, the coronary vein on the left heart surface and the right ventricle, which are connected to a pacemaker implanted under the subclavian skin. The electrical impulses from the pacemaker, through the electrodes, cause synchronized contractions in the left ventricle and the left and right ventricles, and coordinated atrioventricular contractions, resulting in an increase in beat volume, a decrease in regurgitation and an improvement in heart failure. Indications for cardiac resynchronization therapy: On the basis of optimal drug therapy, heart failure patients with class III or IV heart function, ejection fraction ≤ 35% on ultrasound, QRS time limit ≥ 120 ms on ECG, and sinus rhythm are the best indications for cardiac resynchronization therapy. Patients with concomitant atrial fibrillation or those already on pacing therapy are also suitable for resynchronization therapy.