The most serious heart disease depends on different classifications, which are analyzed as follows: 1. Heart disease in terms of heart failure, the most serious is acute left heart failure, characterized by acute onset, patient respiratory distress and high risk of death; 2. Heart disease in terms of arrhythmia, the most serious is tachyarrhythmia, such as ventricular flutter, ventricular fibrillation, ventricular tachycardia heart rate more than 150 beats/min, supraventricular tachycardia exceeding 200 beats per minute, or severe slow arrhythmias, such as a heartbeat less than 35 beats per minute; 3. Cardiovascular heart disease, the most serious of which is acute myocardial infarction, where the risk of death is particularly high due to acute necrosis of the myocardium caused by acute occlusion of the blood vessels supplying the myocardium; 4. Heart disease related to the myocardium, such as dilated cardiomyopathy and severe hypertrophic obstructive cardiomyopathy, which currently lack of effective treatment and a very high risk of death.