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Figure 3 Mean fibrillatory interval and action potential duration (APD₉₀) were measured in the right atrial appendage in seven patients. For each of these patients, mean fibrillatory interval (x-axis) and APD₉₀ (y-axis) are plotted both before (black boxes) and after (white boxes) verapamil. Both mean fibrillatory intervals as well as APD₉₀ shortened significantly in each patient. The relationship between mean fibrillatory interval and APD₉₀ is linear both before and after verapamil administration, and the relationship between both parameters remains unchanged.