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Extended pacing. The heart was paced for extended periods (1-5 minutes) in three hearts. The TTL trigger signal from the laser (red) and the ECG recording (blue) show OP at 2.5 Hz for over 90 seconds without skipping a beat. The dotted lines delineate a region that was expanded and shown directly above the traces to clearly visualize the synchronization of the laser pulses and ECG traces. Extended pacing beyond 5 minutes was not be reliably maintained.
