An isolated heart preparation in which essentially normal pumping activity of all four chambers of the heart is preserved, allowing for the use of the preparation in conjunction with investigations of electrode leads, catheters, cardiac implants and other medical devices intended to be used in or on a beating heart. The preparation may also be employed to investigate heart functions, in the presence or absence of such medical devices. In order to allow for visualization of heart structures and devices located within the chambers of the heart, a clear perfusate such as a modified Krebs buffer solution with oxygenation is circulated through all four chambers of the heart and the coronary vasculature. The preparation and recordings of the preparation may be used in conjunction with the design, development and evaluation of devices for use in or on the heart, as well as for use as an investigational and teaching aid to assist physicians and students in understanding the operation of the heart.