The syringe is either prepacked with a small amount of heparin to prevent coagulation, or must be heparinised, by drawing up a small amount of heparin and squirting it out again..
A syringe can be supplied with a minimal dose of heparin beforehand to inhibit blood coagulation, or alternatively, the syringe needs to be treated with a small amount of heparin by injecting some into the barrel and then ejecting it.