Vagus stimulation with different frequency and increasing current Approximately 10-second long pulse trains with intensities ic of 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 mA at different frequencies of stimulation (10Hz, 20Hz and 30Hz) will be delivered to aforementioned GTE1 until the absence of cardiac contraction occurred. VNS will be terminated instantly after the absence of cardiac contraction was noticed. The time interval between different two simulations will be at least 2 minute or lasted till heart rate or SAP have not reached basal value before stimulation train. Stimulation will be recorded on the same system as ECG, SAP, PAP, CVP and PAO.