A 40mmHg difference in blood pressure between the two arms is not normal. It may be the existence of cardiovascular disease, it is recommended that timely examination, otherwise you will miss the best period of treatment. The two arms of the blood pressure in normal times will have a certain difference, but according to relevant research found that the general will not be 40mmHg difference. under normal circumstances, the two arms of the blood pressure is usually 10-20mmHg difference. the two arms of the blood pressure difference of 40mmHg may be caused by one side of the blood vessel blockage, so it is recommended to go to the hospital in a timely manner to be examined. Cardiovascular diseases such as coronary heart disease and atherosclerosis, which tend to cause narrowing of the blood vessels and affect the blood flow rate, may lead to a difference in blood pressure of 40mmHg between the two arms, which can be determined by blood pressure tests and blood tests according to the instructions of a doctor. It is recommended that the cause of a 40mmHg difference in blood pressure between the two arms should be examined actively and then treated.