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Sir,—In a recent article, Biffi et al concluded that treatment guided by head up tilting is a reliable method of treating severely symptomatic and high risk patients with malignant vasovagal syndrome.1 They also found metoprolol to be superior to clonidine treatment according to their protocol. Their “pharmacological test” comprised isoprenaline infusion in five progressive steps, from 1–5 μg/min at 80° head up tilt. The specificity of isoprenaline challenge with steep angles of head up testing has been questioned. Natale et al investigated the effects of both differing degrees of head up tilt and progressive rates of isoprenaline infusion in normal volunteers with no history of syncope or presyncope.2 Testing at a 70° angle with a low dose isoprenaline infusion provided an adequate specificity of 88%, this fell to 60% during 80° head up testing. Limiting test duration at 80° to 10 minutes would have reduced the false positive rate to 16%. Furthermore, increasing the dose of isoprenaline to …