The isolated heart apparatus serves the dual role of allowing for operation in both the Langendorff and working modes. Constant pressure Langendorff perfusion of the coronaries can easily be modified to allow the heart to self-perfuse by simply inhibiting the flow of buffer through the "Langendorff Bypass".

During Langendorff mode perfusion, the left side afterload is held constant and the flow through the coronaries is determined by dilation or constriction of the coronary arteries. The right and left side holding chambers are closed so there is no flow into the heart by way of the inferior vena cava or pulmonary vein. After the buffer exits the coronary system by way of the coronary sinus located in the right atrium, the buffer flow proceeds into the right ventricle and is ejected out the pulmonary artery.

During working mode the flow through the heart is normally determined by the intrinsic heart rate and the contractility of the heart. The intrinsic heart rate can be modified by altering the temperature of the buffer or via the addition of pharmacological agents. By providing near physiological preload and afterload pressures, the apparatus can allow a heart to function in an almost a one-to-one re-creation of the in situ heart for experimentally useful periods of time (up to hours).