Effect of Ezetimibe on Platelet Aggregation and LDL Tendency to Peroxidation

Inclusion Criteria: 1. Hypercholesterolemic patients on stable simvastatin dose for at least one month. 2. Age ≥18 years on stable AHA step 1 diet. 3. Patients without CHD or with one risk factors ; LDL \> 130 mg/dL and for Patients with CHD or CHD risk equivalent(clinical manifestations of non-coronary forms of atherosclerotic disease) or with 2 risk f actors (cigarette smoking, hypertension (BP ≥140/90 mm Hg or on antihypertensive medication), low HDL cholesterol (\<40 mg/dL), family history of premature CHD;LDL\>100 mg/dL 4. Patients 'on at least simvastatin treatment of 20 mg per day. 5. CPK, ALT and AST \< 1.5 X upper limit of normal at baseline. Exclusion Criteria: 1. Women currently receiving cyclical hormones. 2. Treatment with psyllium, other fiber based laxatives, phytosterol margarines, or other OTCs that affect serum lipids, unless treated with a stable regimen for \> 6 weeks and the patient agrees to continue this regimen for the duration of the trial. 3. Oral corticosteroids unless used as replacement therapy for pituitary/adrenal disease and a stable regimen for at least 6 weeks. 4. Lipid lowering agents including fish oils and QUESTRAN taken within 6 weeks. 5. Active coronary heart disease: unstable angina, acute myocardial infarction, CABG or PTCA within the last 3 months. 6. Women with childbearing potential unless on safe contraception. 7. Psychiatric disease with defect in judgement. 8. Severe renal or hepatic disease. 9. Uncontrolled hypo- or hyperthyroidism. 10. Contraindication for ezetimibe or simvastatin treatment. The patients will continue on their treatment with simvastatin for 6 weeks, and then the patients will be treated by the same dose of simvastatin combined with ezetimibe 10 mg/day for other 6 weeks.