A heparin lock is technique performed in order to prevent blood coagulation in the needle detained in the vessel, or a catheter. In Japan, when we perform a heparin lock, a heparin injection is diluted with physiological salt solution before use. We need to use prefilled syringes with diluted heparin. We received a sample of this product. We investigated the user-friendliness of the product. From our results, the prefilled syringe with the diluted heparin was found to be useful. Furthermore, when we use the prefilled syringe with diluted heparin, patient safety is increased.