Apparatus, comprising: a catheter , located in a heart of a subject and configured to: receive a first group of electrocardiograph (ECG) signals derived from a single heartbeat and generated at a respective plurality of electrodes on the catheter, and receive a second group of ECG signals derived from a subsequent single heartbeat and generated at the plurality of electrodes; a processor configured to: formulate a template relating times of annotations of the first group of the ECG signals, and assign the template an index, calculate times of annotations of the second group of ECG signals, formulate a comparison between the template and the times of annotations of the second group, and when the comparison indicates that the times of annotations of the second group correspond to the template, assign the index to the second group of ECG signals; and a display configured to present graphically an occurrence of the template relative to a timeline representing heartbeats from the heart. a catheter , located in a heart of a subject and configured to: receive a first group of electrocardiograph (ECG) signals derived from a single heartbeat and generated at a respective plurality of electrodes on the catheter, and receive a second group of ECG signals derived from a subsequent single heartbeat and generated at the plurality of electrodes; a processor configured to: formulate a template relating times of annotations of the first group of the ECG signals, and assign the template an index, calculate times of annotations of the second group of ECG signals, formulate a comparison between the template and the times of annotations of the second group, and when the comparison indicates that the times of annotations of the second group correspond to the template, assign the index to the second group of ECG signals; and receive a first group of electrocardiograph (ECG) signals derived from a single heartbeat and generated at a respective plurality of electrodes on the catheter, and receive a second group of ECG signals derived from a subsequent single heartbeat and generated at the plurality of electrodes; a processor configured to: formulate a template relating times of annotations of the first group of the ECG signals, and assign the template an index, calculate times of annotations of the second group of ECG signals, formulate a comparison between the template and the times of annotations of the second group, and when the comparison indicates that the times of annotations of the second group correspond to the template, assign the index to the second group of ECG signals; and formulate a template relating times of annotations of the first group of the ECG signals, and assign the template an index, calculate times of annotations of the second group of ECG signals, formulate a comparison between the template and the times of annotations of the second group, and when the comparison indicates that the times of annotations of the second group correspond to the template, assign the index to the second group of ECG signals; and a display configured to present graphically an occurrence of the template relative to a timeline representing heartbeats from the heart. <EOS>