Normally, the blood pressure in the upper arms of the left and right sides of most people is basically the same, but sometimes the blood pressure in the two upper arms is different, and the difference should not be more than 5-10 mmHg. Some people’s left side is higher than the right side, and some people’s right side is higher than the left side. One theory is that because of the different origins of blood vessels on the right and left sides, the blood pressure in the right arm is generally higher than that in the left arm. If the difference between the two sides of the blood pressure is more than 20 mmHg, you should look for the reason, it is likely to suggest that the blood pressure is lower on the side of the blood vessels there are abnormalities (for example, subclavian artery stenosis due to the proximal stenosis of the subclavian artery, so the patient’s affected side of the upper limb blood pressure is low, the radial artery pulsation is poor or not palpable, the activities of the affected limb, in order to meet the demand for upper limb blood flow, the cerebral blood flow through the vertebral artery countercurrent into the distal arteries of the upper limb arteries (the medical term for the: Arterial Stealing), patients with cerebral ischemia will experience dizziness and discomfort, and in severe cases, they may faint or even have a cerebral infarction. (In addition, young people may be due to multiple aortitis or congenital arterial malformations). Therefore, if it is the first time to measure blood pressure, you should measure the blood pressure on both sides of the left and right arms at the same time. If the blood pressure on both sides is the same or the difference is less than 10 mmHg, then it is a normal phenomenon, but in the future, when monitoring the blood pressure, it should be based on the higher side of the blood pressure; if the difference between the two sides of the blood pressure is 10-20 mmHg, then in the future, you should strengthen the monitoring, and measure the two sides of the blood pressure every 3 months or so, and observe whether the difference between the two sides increases or not. If the difference in blood pressure between the two sides is more than 20 mmHg, you should consult a doctor for further examination.