An analog or digital processing element and associated method analyses electrograms or electrocardiograms to locate sites potentially appropriate for ablation. The element and method compares a first number of electrogram or electrocardiogram samples recorded over time during a cardiac event of known diagnosis with a second number of paced electrogram or electrocardiogram samples recorded over time. The comparison cross-correlates the first number of electrogram samples with the second number of paced electrogram samples. The element and method generate an output based upon the cross-correlation. The element and method compare the output to a predetermined value to determine whether a pacing site for the paced electrogram or electrocardiogram samples is near to a potential ablation site.