Rhythmic contractile activity, synchronized with pulsatile pressure changes, was recorded from rabbit aorta in vivo. The contractions were locked in frequency to the pulsatile activity of the heart even when the heart was electrically paced to rates as high as 600 cycles per minute; termination of cardiac contractility resulted in their elimination. When the atria and ventricles contracted at different rates, the pulse-synchronized contractions were locked to the atrial rate. Excision of the right atrium, but not the left, resulted in the abolition of pulse-synchronized contractions. It is concluded that common pacemaker controls cardiac and vascular contractility, coordinating events in the two tissues.
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