This is a prospective, multi-center, superiority study of parallel design. Patients are enrolled if they are older than 18 years old, are scheduled for 5 or 6 Fr diagnostic coronary angiography and the interventional cardiologist is willing to proceed with radial access. Patients are randomized before diagnostic catheterization to receive intravenously either 100IU/Kg or 50 IU/Kg of unfractionated heparin (UFH) in a 1:1 ratio. Patients are discharged usually within 4 to 6 hours after coronary angiography.

Radial artery in each patient is evaluated either in-hospital or during a subsequent visit by one physician who is blinded to the actual antithrombotic treatment given. Radial artery is considered occluded if it exhibits ultrasonographically no antegrade flow signal both at baseline and after reevaluation on a second occasion, within 30 days after the index procedure. Initially patent arteries will not be reexamined and are thought to remain permanently patent. The investigators also monitor major bleeding (defined as ≥ 5g/dL decrease in hemoglobin or ≥15% decrease in hematocrit or any life-threatening bleeding (confirmed by MRI or computed tomography) and large local hematomas of the forearm (defined as those extending beyond the forearm).

Inclusion Criteria:

• Older than 18 years old
• Scheduled for 5 or 6 Fr diagnostic coronary angiography
• The interventional cardiologist is willing to proceed with radial access
• Written informed consent

Exclusion Criteria:

Before randomization

• chronic hemodialysis
• oral anticoagulation
• hemodynamic instability
• severe dermo-myoskeletal forearm deformities
• history of CABG and bilateral use of either the internal mammary or radial artery
• history of CABG and ipsilateral use of both the internal mammary and radial artery
• admission for elective PCI After randomization
• crossover to another arterial access site is required
• ad hoc PCI