The invention relates to a heart monitor for processing input signals representing periodically reoccurring events in a sequence of heart cycles, in particular ECG signals. According to the invention graphical data representing a scatter plot of at least two dimensions, one dimension representing interval duration (e.g. RR interval) or its inverse and the other dimension representing change of duration or its inverse, respectively, are generated. The scatter plot comprises data points of which each data point represents heart interval duration or its inverse plotted against the change of duration with respect to a neighboring interval or the inverse of said change respectively. An analyzer stage is adapted to detect cluster of data points and generate a rhythm classification output signal.
