Clopidogrel pre-treatment before planned percutaneous coronary intervention was proved to reduce periprocedural complications. However, the vast majority of patients in the current interventional cardiology practice do not undergo planned PCI, but rather "ad-hoc" PCI performed immediately after coronary angiography . Whether clopidogrel should be administered as pre-treatment to all patients undergoing elective CAG with the aim to ensure therapeutic levels at the time of possible ad-hoc PCI is not known.