Electrocardiogram (EGG) is the recorded electrical potentials generated by the heart during a cardiac cycle. Gardiac abnormalities cause unknown current flows leading to strange waveform morphologies in the recorded EGG. Some of these abnormalities are only visible when the heart is under stress. Exercise EGG is conducted for this reason. Ischemia is one of the important cardiac abnormalities and is the focus of our study. It occurs when a part of the heart tissue dies or is injured. QT dispersion (QTd) is a proposed method for diagnosing Ischemia. The classical deflnition for QTd is the difference between the maximum and the minimum QT intervals within the 12 leads. In this study the effect of exercise on QT dispersion (QTd) is studied and whether QTd could give significant information for diagnosing patients with ischemic heart disease is investigated. A new method for measuring QT interval is developed and is compared with previous methods. QTd is measured on average beats calculated for 10 seconds intervals throughout the exercise ECG test and a trend curve which we call QTd, is generated. Several decision rules for the diagnosis of cardiac patients are proposed by analyzing these QTd trend curves and the accompanying heart rate curves. It is shown that despite the improvement in QT interval measurements, none of the decision rules proved to be a clinically useful discriminate of cardiac patients, with sufficient confidence.