The novel endomyocardial biopsy approach described here could facilitate the study of some human pathologies for which tissue specimens are currently unavailable. Electrical and mechanical characteristics such as rat responses, effect of extracellular calcium concentration changes and beta-adrenergic tone were similar to those determined for other human ventricular tissues, indicating that endomyocardial biopsies are suitable for physiological studies. This new source of cardiac tissues should facilitate the investigation of cellular mechanisms involved in the development of previously inaccessible human diseases.