To predict responders to metoprolol before treatment, we used to test plasma norepinephrine, copeptin and CNP levels, attempting to find predictive measures for therapeutic responders to metoprolol before treatment of children with POTS (Benditt and Chen, 2012; Zhang et al., 2014; Zhao et al., 2014; Lin et al., 2015b). Here, AVP is linked to postural orthostatic tachycardia syndrome.