Supplemental Video S2

Initiation of re-entrant tachycardia in the isolated atria of a 6 month old spontaneously hypertensive rat. S1-S1 pacing was performed at 20 ms intervals from the right atrial appendage to trigger the arrhythmia. Optical action potentials on the right from the RAA (blue), LAA (orange) and LAR(green) have been averaged across regions indicated on the left. Vertical black bars indicate pacing signal.