A fast and slow heartbeat is commonly associated with various arrhythmias, the causes of which include physiologic and pathologic ones. Pathologic causes commonly include atrial fibrillation, paroxysmal supraventricular tachycardia, and slow-fast syndrome. In a quiet state, the number of heartbeats per minute in a normal adult is usually 60~100. Physiological causes include: fast and slow heartbeat is sometimes a normal phenomenon, emotional excitement, insufficient rest time, intense exercise can cause this phenomenon, can be relieved by adequate rest and emotional stability. Pathological reasons include: patients with atrial fibrillation may have heart rates that vary in speed, pulse strengths and weaknesses, and completely irregular heart rates. Paroxysmal supraventricular tachycardia may be characterized by palpitations, tachycardia, sudden stops, and variable duration. In addition, a special type of arrhythmia called slow-fast syndrome can manifest clinically as a fast heartbeat and a slow heartbeat at the same time. If the patient feels obviously uncomfortable, it is recommended to go to the hospital immediately for a 24-hour dynamic electrocardiogram to identify the cause of the disease and then actively treat it.