Without neurohumoral effects, WT hearts showed a regular rhythm with 125 ± 20 beats per minute, and the Pkd2-KO hearts had arrhythmic heart rate of 127 ± 22 beats per minute evidence from atrial fibrillation or atrioventricular block characterized by irregular R-R intervals. The gene discussed is PKD2; the disease is atrioventricular block.