This book on investigative electrocardiography is addressed to investigators who are using electrocardiology as a research tool in epidemiological or clinical research or in investigations on possible adverse responses of new pharmacological agents. The primary emphasis of the book is on prognostic implications of ECG abnormalities in the conditions covered, including the prevalence and incidence of ECG abnormalities in contrasting populations. We excluded from our book cardiac disorders with a relatively low population pre- lence that otherwise may be of great clinical interest. We also decided to exclude acute myocardial infarction because we had only limited resources available on this topic from our population studies and from those clinical trials in which we have personally p- ticipated in the classi? cation of trial endpoints within the framework of an ECG research center. Clinical trials are a relatively new area of electrocardiology. However, electrocard- graphy has become a most valuable research tool in clinical trials and in investigations on morbidity and mortality risk associated with various clinical and subclinical con- tions. It has also become a crucial research tool in investigating adverse cardiac events associated with administration of new drugs. Evaluation of QT prolongation plays a central role in these investigations. As a possible marker of malignant arrhythmias, it is used by regulating agencies in their decision process for approval of new pharmacolo- cal agents.