What is the supranormal period cardiovascular?

Supranormal period or tachycardia occurs because the AV nodal conduction time shortens after vagal blockade, and the sinus rate increase. There is an increase in the myocardial contractile force (i.e., positive inotropy) but, because the heart rate exceeds the critical level for the filling time of the ventricles (i.e., about 150 beats/min), the ejection volume becomes smaller. The rise in mean arterial pressure is due to the increase in heart rate.