There are two reasons why the heart rate accelerates after blood donation: First, because when donating blood, the donor can see the needle piercing his or her body and observe the process of blood flowing out, which inevitably generates a certain amount of nervousness. Secondly, as the blood volume of the body loses between 200-400ml after blood donation, the blood volume decreases and the heart system reacts by increasing to compensate for the decrease in blood volume, resulting in a faster heart rate, and in severe cases, panic and chest tightness, but it is relatively mild and not easily detectable. Therefore, after blood donation, it is important to take proper rest, avoid strenuous activities, rest more and supplement nutrition in order to replenish the lost red blood cells and plasma in a short period of time.