This study will assess whether co-administration of ezetimibe 10 mg with simvastatin 20 mg will be more effective than treatment with simvastatin 20 mg alone in reducing LDL-C concentrations when administered for 6 weeks.

Inclusion Criteria:

• >=18 years and <= 75 years of age
• LDL-C concentration >= 3.3 mmol/L (130 mg/dL) to <= 4.9 mmol/L (190 mg/dL) at baseline.
• Triglyceride concentration <3.99 mmol/L (350 mg/dL) at baseline.
• Documented coronary heart disease (CHD), which will include one or more of the following features: documented stable angina (with evidence of ischemia on exercise testing); history of MI; history of PCI (primarily PTCA with or without stent replacement); symptomatic peripheral vascular disease; documented history of atherothrombotic cerebrovascular disease; and/or documented history of non-Q wave MI.
• Stable weight history for at least 4 weeks prior to entry into study at baseline.
• Female subjects of childbearing potential must be using an acceptable method of birth control or be surgically sterilized.

Exclusion Criteria:

• Body mass index (BMI) >=35 kg/m^2 at baseline.
• Subjects whose liver transaminases (ALT, AST) are >1.5 times the upper limit of normal and with active liver diseases at baseline.
• Subjects with evidence of current myopathy (including subjects with CK>1.5 times above the upper limit of normal) at baseline.
• Subjects with clinical laboratory tests (CBC, blood chemistries, urinalysis) outside the normal range that are clinically acceptable to the investigator at baseline.
• Subjects with Type II diabetes mellitus who are poorly controlled (HbA1c>9%) or newly diagnosed (within 3 months) or who have had a change in anti-diabetic therapy within 3 months of baseline.
• Subjects with Type I diabetes mellitus who have not been on a stable insulin regimen for 3 months prior to baseline, or who have a recent history of repeated hypoglycaemia or unstable glycaemic control.
• Subjects who have known hypersensitivity to HMG-CoA reductase inhibitors.
• Female subjects who consume >14 units and male subjects who consume >21 units of alcohol per week.
• Female subjects who are pregnant or breast feeding.
• Subjects who have not observed the designated washout periods for any of the prohibited medications.