A brief historical review of the concepts that have existed in myocarditis in the nineteenth and twentieth centuries is presented. The establishment of this entity is linked with the milestones of discovery in medicine, especially the development of the stethoscope, the microscope, and the science of bacteriology. Yet, despite these advances, chronic myocarditis was still a common diagnosis up to about the third decade of the twentieth century and included conditions such as hypertension. Evidence of myocarditis was often not present or had not been sought. It became clear that the term “myocarditis” was indiscriminately used and, following admonition from such authorities as Sir Thomas Lewis and Dr. Paul White, resulted in under-diagnosis of myocarditis. Clinically, the signs and symptoms of myocarditis are nonspecific and morphologic recognition is also fraught with many pitfalls, among which the distinction from ischemic heart disease and myocardial infarction has to be made. With the introduction of the bioptome, clearer concepts have developed and the latest definition is cited. Sequential biopsies have also permitted a classification into active, healing, and healed myocarditis to be made. Examination of fresh endomyocardial tissue, obtained by bioptome, has also shed light on the pathogenetic mechanisms of two of the three forms of cardiomyopathy, namely, dilated (congestive) cardiomyopathy and endomyocardial disease associated with an eosinophilia. Clear concepts are essential in diagnosing this condition. These are now emerging through morphologic examination of fresh endomyocardial tissue.