To evaluate the effect of treatment with rifalazil versus placebo taken once weekly for 12 weeks on carotid atherosclerotic disease progression in patients who test positive for Chlamydia pneumoniae. Measurements of the carotid artery wall (intima-media thickness) and plaque characteristics will be evaluated with high-resolution magnetic resonance imaging (MRI) and carotid ultrasound. at Baseline and at 6,12 and 18 months following initiation of drug treatment in Chlamydia pneumoniae seropositive patients with a history of atherosclerotic disease. Biomarkers will be collected throughout the study. Safety will be evaluated by the collection and analysis of laboratory parameters, vital signs, electrocardiograms, physical examination and adverse events. Seventy two patients will be enrolled in this study. There will be a total of approximately 7-9 visits which will occur over an 18 month period.