The weather is too hot blood pressure will still be a little low, the high temperature environment will make the skin vasodilatation, so blood pressure can be slightly lower, peripheral resistance decreases. The amount of blood ejected from the heart remains the same, when the peripheral resistance decreases, the heart diastolic in which the blood flow to the periphery slows down, the heart diastolic end of the presence of the aorta blood flow increases, diastolic blood pressure will be significantly higher. In the systolic phase of the heart due to the increase in arterial blood pressure, blood flow is accelerated, systolic pressure is high, but not as pronounced as the increase in diastolic pressure, and the pulse pressure difference is reduced. Because the diastolic blood pressure is mainly determined by the size of peripheral resistance, when the caliber of resistance vessels becomes smaller and blood viscosity increases, peripheral resistance increases and blood pressure naturally rises.