Having an MI can cause changes in many areas of the heart. An ECG or EKG is a tracing of the electrical pathway through the heart. Changes in that electrical cause changes in the EKG. The location of the changes depends on where the myocardial infarction (MI) occured. An acute MI, meaning one that has just occured or is happening right at that moment, most often causes changes in the portion of the tracing called the ST segment. Elevations, depressions and prolonged reactions in this segment are indicative of myocardial cell damage that occurs in an MI.