The study is an investigator-sponsored, prospective, multicenter, randomized, open-label study designed to compare efficacy and safety between bivalirudin and heparin in elderly patients with acute coronary syndrome undergoing elective percutaneous coronary intervention.

Inclusion Criteria:

• Age ≥75 years old;
• Planned elective PCI for patients with acute coronary syndrome;
• Life expectancy ≥ 1 year;
• Provide written informed consent.

Exclusion Criteria:

• Contraindications to angiography or PCI;
• Active bleeding or bleeding constitution, bleeding tendency, including GI or urinary tract hemorrhage (3 months), cerebral hemorrhage (6 months) or cerebral infarction history (3 months), etc;
• Other disease may lead to vascular lesions and secondary bleeding factors (such as active gastric ulcer, active ulcerative colitis, intra-cerebral mass, aneurysm, etc.);
• Severe renal insufficiency (eGFR < 30 mL/min/ 1.73 m2);
• Elevated AST, ALT level higher than three times of the normal upper limit;
• Advanced heart failure (NYHA classification grading of cardiac function ≥Ⅲ) Complicated with immune system diseases#
• Abnormal hematopoietic system: platelet count < 100 × 109 / L or >700 × 109 / L, white blood cell count < 3×109/L etc;
• Suffering from acute infections ,infectious diseases or other serious diseases, such as malignant tumors;
• Known intolerance, or contraindication to any antithrombotic medication
• Known allergy to the study drugs and instruments (UFH, bivalirudin, aspirin and clopidogrel, stainless steel, contrast agents, etc.), or those allergic constitution.
• Non-cardiac co-morbid conditions are present that may result in protocol non-compliance;
• Patients who are actively participating in another drug or device investigational study, which have not completed the primary endpoint follow-up period;
• Patient's inability to fully cooperate with the study protocol