Methods of processing electrocardiogram (ECG) data, and related systems, generate a beat-to-beat HR scatter plot/display for evaluation by a medical professional for diagnosis of cardiac irregularities. A method of processing ECG data includes processing ECG data recorded for a patient over a monitored time period to identify beat-to-beat intervals. Heart rates are calculated for the beat-to-beat intervals. The calculated heart rates include a respective heart rate for each of the beat-to-beat intervals. The calculated heart rates are displayed and/or plotted for an output period of time.
