Despite refinements in immunosuppressive therapy, acute allograft rejection remains a major cause of mortality in heart transplant recipients. The high reliability, noninvasiveness, possibility of day-to-day monitoring, absence of interobserver variability, and cost effectiveness are essential components of the ideal diagnostic method for the detection of allograft rejection. This paper reviews the experimental and clinically established methods for the diagnosis of acute allograft rejection. The most promising tools seem to be electrophysiologic, because these tools provide the potential for continuous noninvasive distant rejection monitoring, and echocardiographic techniques that enable the safe assessment of changes in cardiac structure and function and further reduce the need for endomyocardial biopsy and, more importantly, provide a better definition of the threshold for antirejection treatment. Additional research and refinements of techniques and evaluation in prospective randomized multicenter studies are needed to further advance the use of noninvasive methods for diagnosis of heart graft rejection.