The primary aim of the Core Electrocardiographic Laboratory (CEL) in the Bypass Angioplasty Revascularization Investigation (BARI) trial is: (1) to oversee the quality of rest and exercise ECG data; (2) classify rest ECGs according to Minnesota code and analyze exercise ECG data; (3) classify suspected myocardial infarct events, a major end point in BARI. All protocol rest ECGs (annual, procedure, and suspected MI events), data forms for suspected myocardial infarct events, and protocol exercise electrocardiograms will be sent to the CEL for analysis. The CEL is mandatory to minimize the possibility of under or over reporting incident rates of myocardial infarction from individual clinical units and reduce the potential for major intercenter variability in the detection of myocardial infarction. The need for core ECG laboratories in large multicenter clinical trials is well established. The St. Louis University CEL has been funded since December of 1988 to support the BARI clinical effort and has development customized software for exercise ECG analysis, software which automatically determine Minnesota code based on a measurement matrix and software which permits serial comparison of rest electrocardiograms. The analyzed ECG data are electronically transmitted to the DATA Coordinating Center. In this competitive grant renewal which will permit completion of five year follow-up for all patients and extended follow up for 10 years after enrollment, the St. Louis University CEL is requesting continued funding to permit all of the above as well as classify suspected myocardial infarct events based on clinical presentation, cardiac enzyme data, and ECG analysis, blinded to treatment assignment. A 2 step worsening in Minnesota Q wave code only is used to determine procedure related myocardial infarcts whereas for nonprocedure related infarcts, the diagnosis of infarction is based on 2 step worsening in Minnesota Q wave code, a history of chest pain greater than 20 minutes, and serial cardiac enzyme data in which total CK exceeds twice normal and CK-MB is positive with MB taking precedence over total CK. The St. Louis University CEL has years of experience using the Minnesota code and in analyzing exercise ECG documents and classifying myocardial infarct/ischemic events, and serves as an ECG and MI classification core facility for several NIH sponsored clinical trials.