We were particularly pleased to compile this volume entitled 'Clinical Aspects of Cardiac Arrhythmias'. Recent years have seen the publication of many textbooks on cardiac arrhythmias, some of which concentrate on one particular aspect such as drug management, electrocardiographic appearances, electrophysiological evaluation etc; and others of which are the collated reports of symposia, often dealing with detailed con­ siderations of highly specialised problems. Most of the larger more comprehensive texts have devoted a substantial proportion to basic considerations and experimental observations, far removed from the clinical arena. When asked to contribute to the series 'Current Status of Clinical Cardiology' we felt that the clinical aspects of cardiac arrhyth­ mias should be emphasized, and that the text should be as comprehensive as possible within the limitations of a single volume in this series. This comprehensive but clinical approach has necessitated the inclusion of certain subjects such as the mechanisms of tachycardia, metabolic aspects of cardiac arrhythmias and reperfusion arrhythmias, which are not directly or exclusively clinical. However, the rapid advances in these areas in recent years are likely to have increasingly important clinical con seq uences. Although the epidemiology of clinical arrhythmias is difficult to dis­ cover, it is widely appreciated that arrhythmias are commonplace.