Stock blood is stored for a long time and the energy in the red blood cells is depleted, causing massive lysis of the red blood cells, which releases the potassium from the cells. In general, potassium can increase 4-5 times for two-week stored blood and up to 10 times for three-week stored blood, which can lead to hyperkalemia when large amounts of blood are transfused. Hyperkalemia is very dangerous, as the patient may suffer from chest tightness, panic attacks, slow heart rate, or even severe cardiac arrest and death. Therefore, it is important to monitor the blood potassium when transfusing long-preserved blood stocks and to provide symptomatic treatment according to the blood potassium situation.