Synchronization of atria and ventricles resembling the clinical phenomenon of isorhythmic A-V dissociation could be produced in 45 of 48 anesthetized cats by stimulating the ventricles slightly above the spontaneous sinus rate. A fall in aortic pressure connected with an increase in right atrial pressure always occurred when ventricular contraction preceded atrial contraction. Synchronization could be prevented neither by vagotomy or β-adenolysis nor by keeping the right atrial or aortic pressure at a constant level. Stretching of the sinus node fibers during atrial contraction against a closed tricuspid valve is regarded as the crucial mechanism responsible for A-V synchronization.
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