Heparin is the first choice of anticoagulation drug for primary PCI of STEMI patients. However, the priority of use of hepairn in first medical contact or in Cathlab has not yet studied. Previous study revealed early use of antithrombotic drugs could improve patient's survival. Here we supposed that use of heparin at first medical contact could increase the TIMI flow 3 grade ratio in STEMI patients and improve patient's survival and/or reduce MACE rather than in Cathlab.

This study will recruit 944 STEMI patients undergoing primary PCI with the symptom onset within 12 hours in 36 hospitals in Hubei Province, China. The patients will be 1:1 randomly assigned to the intervention group (IG) and control group (CG). Patients in IG will be intravenously administrated with sodium heparin (100U/Kg) at first medical contact, while patients in CG will be administrated with sodium heparin (100U/Kg) through catheter sheath in the CathLab.

Inclusion Criteria:

STEMI patient; Symptom onset in 12 hours; Intended to perform PPCI. Exclusion Criteria:Active bleeding; Life expectancy less than 1 year; History of heparin-induced thrombocytopenia; Mechanical complication of MI (VSR, acute MR); History of CABG; On Coagulation drugs; CPR before randomization; Pregnant or lactating woman;Refused to sign the Informed Consent Form.

Inclusion Criteria:

• STEMI patient; Symptom onset in 12 hours; Intended to perform PPCI

Exclusion Criteria:

• Active bleeding; Life expectancy less than 1 year; History of heparin-induced thrombocytopenia; Mechanical complication of MI (VSR, acute MR); History of CABG; On Coagulation drugs; CPR before randomization; Pregnant or lactating woman.