It is not normal for the left hand blood pressure to be 20mmHg higher than the right hand. Normally it is about 5~10mmHg higher, which may be a manifestation of aortic constriction, aortic coarctation aneurysm, subclavian artery steal syndrome and so on. For the human body, when measuring the blood pressure of the right and left hands, under normal circumstances, there is indeed a certain difference, generally high left and low right, the left side is higher than the right side of 5~10mmHg. However, if the blood pressure of the left hand is higher than that of the right hand by 20mmHg, it is anomalous, and it may be the symptomatic manifestation of the following lesions. 1. Aortic narrowing. Aortic constriction may occur when ductus arteriosus fibrosis occurs proximal to the left subclavian artery, leading to aortic isthmus and aortic isthmus constriction. Arterial narrowing causes an abnormal reduction in blood flow to the brachial artery in the right arm, which affects blood pressure, making the blood pressure in the right arm significantly lower than the left. 2. Aortic coarctation aneurysm. Aortic coarctation aneurysm affects blood flow, resulting in unilateral limb blood flow, causing the left arm blood pressure to be 20mmHg higher than that of the right arm. 3. Subclavian artery steal syndrome. Due to the stenosis of the proximal segment of the subclavian artery, atherosclerosis and other diseases may cause compensatory reflux of the vertebral artery, abnormal blood supply deficiency of the vertebral subterranean artery, which in turn leads to insufficient blood supply of the right brachial artery and a drop in blood pressure. If you find that the left hand blood pressure is 20mmHg higher than the right hand, it is recommended that you should consult a doctor in time, and strictly follow the doctor’s instructions for examination and treatment, so as to avoid delaying the condition.