Cardiac asystole during HUTT has been described by some investigators as a benign finding with no major sequelae. Our aim in this study is to correlate the severity of clinical symptoms and physiologic findings prior and during the asystole occurrence. This is a retrospective study review of 536 patients who underwent HUTT for dysautonomia symptoms for the last 3 years. HUTT in our institution consists of 10 min in supine, 30 min of head up at 70°, and recline to supine for 10 min. Physiologic parameters recorded include continuous heart rate, BP, cardiac stroke volume, brain blood flow by near-infra red spectroscopy, sympathetic and parasympathetic tones. Patients' complaints and signs during HUTT were recorded. Follow-up was conducted up to 34 months. Cardiac asystole was defined as the absence of ventricular activity for ≥3 s with cessation of BP signal for the same period on the monitor. Of the 536 patients studied, 25 patients developed cardiac asystole (4.7%). The asystolic group age was 15.1 + 3.8 years and weighed 56.7 + 21 kg. All the patients fainted and were not able to complete the test with average head up time of 13.8 + 7.1 min. The cardiac asystole duration was 9.2 + 5.8 s. Sixteen patients developed convulsions during the asystole. There was sudden intense vagal tone prior to and during the asystole. Brain perfusion was significantly decreased in all the patients after head up and sharply dropped by 20-35% in patients who developed convulsions. All patients completely recovered their consciousness after reposition to supine. During recovery, there was overshoot of the brain perfusion above the baseline for several minutes and the HR returned to baseline. Follow-up of these patients: only one patient had a single lead pacemaker, otherwise the 24 patients had no cardiac pacing and were treated by medical therapy. During mean follow-up of 19 + 10 months, five patients developed syncope which resolved after optimizing medical therapy. Cardiac asystole due to neurocardiogenic syncope and dysautonomia has high association with brain anoxia that can lead to convulsions. Such patients require intense medical therapy and close observation with possible intervention by cardiac pacing if prolonged asystole occurs. There is a concern of consequence future brain function.