A blood pressure of 80/42mmHg is dangerous. The normal range of blood pressure for a normal adult is above 90mmHg for high pressure and above 60mmHg for low pressure. If both high pressure and low pressure are below the normal range, it means that the effective circulating blood volume is insufficient to supply the important tissues and organs, which may be life-threatening. The blood pressure of 80/42mmHg is already significantly lower than the normal range, and if left unchecked, a continuous drop in blood pressure will lead to shock. The cause should be identified and treated immediately to prevent further aggravation of the condition. Therefore, if you find blood pressure 80/42mmHg, do not diagnose yourself according to a single result, you should consult a doctor immediately, need to cooperate with the doctor to improve the relevant examination, after a clear diagnosis, strictly in accordance with the doctor’s instructions for treatment.