HE CLASSIC IMPLANTATION technique for donor hearts utilizes anastomoses of the aorta, the pulmonary artery, and the left and right atrium. The importance of atrial myocardium in heart transplantation is due to the fact that large parts of the recipient left and right atrium remain in situ, providing a site to suture donor and recipient atria. However, while the status of the ventricular myocardium in end-stage failing hearts is well characterized, little is known about atrial pathophysiology. If one supposes that the recipient atrial myocardium is severely altered, it seems reasonable to hypothesize that potential pathophysiological alterations may affect the new donor organ when donor and recipient myocardium are connected by an atrial suture line. In an attempt to characterize contractile function in more detail, the atrial Frank-Starling mechanism and the atrial force-frequency relationship were analyzed in donor and recipient hearts using atrial trabeculae. The Frank-Starling mechanism states that an increase in diastolic filling causes an increase in peak systolic atrial pressure. The forcefrequency relationship (or “staircase phenomenon) describes an increase in force output upon increasing stimulation frequencies up to an optimal level. Controversal results have been reported regarding the applicability of the Frank-Starling mechanism in failing