The sudden slowing of the heartbeat is related to physiological causes such as increased excitability of the vagus nerve and excessive reserve capacity of the heart, as well as pathological causes such as organic diseases of the heart. 1. Physiological reasons: When the organism is sleeping or resting, in order to ensure that the important organs get sufficient rest, the blood pressure will be lowered, the vagus nerve will slow down the heart rate, and the heartbeat will become slower. For people with a high level of physical activity, the heart rate will also slow down due to the higher reserve capacity of the heart than normal people and high pulse output. 2. Pathological causes: Organic diseases of the heart, such as heart valve disease, sick sinus node syndrome, etc., can lead to a decline in the function of the sinus node, arrhythmia, and bradycardia. If you find that the heartbeat is too slow, there may be other reasons, it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, and then give targeted treatment or treatment under the guidance of the doctor.