Endomyocardial biopsy (EMB) provides a safe, simple method of gathering unique information. Although the role of EMB continues to evolve rapidly, present consensus includes the following indications, based on the ability of EMB to provide diagnoses unobtainable by other means: assessment of early rejection following cardiac transplantation; determination of myocarditis as etiology of clinically obscure cardiac dysfunction; quantification of chemotherapeutic (especially anthracycline) cardiotoxicity; and distinction between constrictive and restrictive heart disease. Each of these indications carries major therapeutic as well as prognostic implications. Methods of processing EMB are presented, complications listed, artifacts described, findings and uses illustrated, and suggestions for future development addressed briefly.