The growth of knowledge of the QT interval of the ECG is reviewed. 1980 was the centennial of the first careful measurements of Burdon-Sanderson and Page, and also the 60th anniversary of Bazett's contribution that established a predictable relation of the QT to heart rate in normal subjects. The waxing and waning of interest in the QT among clinical cardiologists appear to have been related to a low sensitivity and specificity of abnormal QT/rate ratios in many clinical diseases. The QT duration has been established as a valuable measurement, and sometimes the patterns may be nearly pathognomonic of electrolyte disturbances. Alterations from a predicted normal mean may give a clue to disease. The importance of transient dissociation of the predicted QT from the measured QT with rapid changes in heart rate deserves further emphasis. In the publication of data on the duration of QT, the reporting only of the corrected QT (QTc), the index of Bazett, conveys an incomplete picture of the nature of the changes. The prolonged QT pattern in adults should be suspected of being related to drugs first, except when a neurogenic cause is apparent. The idiopathic hereditary syndrome still defies a completely adequate explanation, though neurogenic influences are overtly important. No universal management has been established.