The Bypass Angioplasty Revascularization Investigation (BARI) is a collaborative, randomized, multicenter clinical trial designed to assess the relative efficacy of percutaneous transluminal coronary angioplasty (PTCA) and coronary artery bypass graft (CABG) surgery in patients who require invasive therapy and have coronary anatomy suitable for either procedure. This study will require seven years for completion including phases of one year for protocol development and refinement, two years for patient recruitment, four years for patient follow-up and one year for close-out of the clinical units, data coordinating center and radiographic laboratory. All patients undergoing coronary arteriography at collaborating clinical units because of severe or unstable angina pectoris with or without antecedent myocardial infarction, will be asked to participate in the BARI registry. All patients who qualify, have their attending physician's consent, and satisfy the to be determined inclusion and exclusion criteria of the trial, will be randomized for therapy either with PTCA or CABG. These patients will then be followed for a period of not less than four years utilizing a primary end-point of death and secondary end-points of myocardial infarction, congestive heart failure and recurrent angina pectoris to compare these two groups.