Inclusion Criteria:  Patients aged ≥ 18 years who have a history of stable CHD receiving long-term mono-antiplatelet therapy with aspirin (80 mg once daily) for reducing cardiovascular risk will be recruited from the outpatient clinic.  Exclusion Criteria:  Patients who are currently taking ticlopidine, clopidogrel, dipyridamole or other antiplatelet / antithrombotic agents will not be recruited. Patients who are on regular therapy with anti-inflammatory drugs, or others drugs containing aspirin or non-steroid anti-inflammatory drugs (NSAIDS), or traditional Chinese medicine that have direct effects on the haemostatic system, such as angelica, danshen, garlic, ginger, ginkgo and motherwort will not be included unless they are willing to stop these treatments for at least 2 weeks Patients will not be recruited if they had MI, stroke, coronary artery bypass surgery or other revascularization procedure, unstable angina or angioplasty within 3 months of screening.