ObjectiveTo investigate the roles of nitric oxide (NO) and eNOS in the pathogenesis of vasovagal syncope (VVS). MethodsFourteen children with VVS (group A), 10 children with syncope other than vasovagal (group B) and 20 healthy volunteers (group C) were enrolled. Plasma NO levels in groups A and B were determined before and at the termination of the head-up tilt table test (HUT). The G894T polymorphism within the eNOS gene was determined in the three groups. ResultsPlasma NO levels in group A increased significantly when syncope attacked from 76.7±9.6 μmol/L (before HUT) to 90.0±11.4 μmol/L (P<0.05). After the syncope attack was improved, plasma NO level in group A was significantly reduced. There were no statistical differences in plasma NO levels before and after the HUT in group B. Determining the G894T polymorphism within the eNOS gene showed that group A was associated with a higher incidence of the GT gene type as compared to groups B and C (42.9% vs 10%; P<0.05). ConclusionsPlasma NO may be involved in the pathogenesis of VVS. The increased plasma NO level may be associated with the G894T polymorphism of the eNOS gene.