Twenty five years ago, cardiomyopathies or myocardopathies as they were sometimes called, were in very small print, and often the terms myocarditis and cardiomyopathy were used interchangeably. Now definition and classifi- cation can be precise and terminology has been refined. Although a great deal still has to be learnt about the heart muscle diseases, they have now achieved the status of an important group of cardiovascular disorders. Their importance is out of proportion to their frequency because the cardiomyopathies so often attack young otherwise active and healthy people, and are notable for sudden unexpected death, and for intractable congestive heart failure. They are especially a meance in age groups younger than those most commonly effected by coronary heart disease. This book presents an analysis and review by many experts of the present knowledge about heart muscle diseases and employs the approach to classi- fication and terminology now generally, though not universally, agreed. It will be apparent that much fundamental research must be done now that the clinical problems have been defined. In the future, the collaboration of molecular biologists and other basic scientists will be needed to illuminate the dark places of our ignorance.