Abstract: A method and apparatus for composing a reference heart beat by synchonously summing heart beat signals detected by a high resolution radioactivity distribution detection system for non-invasive measurement of cardiac performance. A plurality of sensing devices form an array for detecting radioactive events emitted from a heart under study. A processor sums heart beat images of a continuous series of detected events and generates a reference heart beat by synchronizing the regrouping of the beat images as a function of the peaks at volumetric end diastole and the image troughs at volumetric end systole. The reference heart beat represents a statistical standard heart beat for the heart under study and defines a base signal for quantative measurements and qualitative analysis of the condition of the subject heart.