Analysis of the ST segment/heart rate slope during exercise testing has been suggested as a method of accurately predicting the presence and severity of coronary artery disease. Exercise tests were performed in 78 patients presenting with the chest pain to determine the maximum ST segment/heart rate slope. In 21 (27%) patients the ST segment/heart rate slope could not be calculated in any electrocardiographic lead. In the remaining 57 (73%) patients the maximum ST segment/heart rate slope accurately predicted the presence or absence of coronary disease in 44 patients (sensitivity 90%, specificity 40%). In addition, the extent of coronary disease was accurately predicted in 24 patients (sensitivity 42%). Thus the maximum ST segment/heart rate slope did not perfectly predict either the presence or the severity of significant coronary artery disease.