The book focuses on one of the most difficult areas of ECG interpretation, that of cardiac arrhythmias. It is a collection of 50 ECGs recorded from patients presenting with a wide QRS complex tachycardia. The differential diagnosis of such a tachycardia includes ventricular tachycardia, supraventricular tachycardia with pre-existing or functional bundle branch block and pre-excited tachycardia. It is extremely important that practitioners, especially those from Emergency Departments, Cardiology Units and Intensive Care Units are able to recognize life-threatening arrhythmias and be familiar with the differential diagnosis of wide QRS complex tachycardias, in order to provide appropriate treatment. The format of the book is focused on teaching: each chapter contains a brief description of the clinical context, an ECG, a question about the nature of the wide QRS complex tachycardia presented on the ECG and a list of 5 possible answers. The correct answer is then provided, with a detailed description of the ECG. References to medical literature for further reading are provided at the end of each chapter. This book will be most useful for medical students, cardiology residents and senior cardiologists, as well as physicians and residents working with arrhythmia patients, such as anesthetists, internal medicine specialists and physicians working in Emergency Departments, or any physicians with a keen interest in improving their ECG interpretation skills.