 There is ample evidence of the importance of blood volume in the pathophysiology of vasovagal syncope. Fludrocortisone acetate is a corticosteroid with a mild enhancement of glucocorticoid activity and a marked increase in mineralocorticoid activity. It has no appreciable glucocorticoid effect at doses between 0.05 to 0.2 mg, which are the commonly used clinical doses for various disorders requiring mineralocorticoid adrenal replacement. The acute actions of fludrocortisone acetate are sodium and water retention, at the expense of urinary potassium excretion. Blood volume expansion with either dietary salt supplementation or fludrocortisone is often recommended by clinicians for the treatment of vasovagal syncope despite a paucity of good evidence for their efficacy. Four clinical studies suggest its utility in the prevention of syncope. Fludrocortisone might decrease the incidence of vasovagal syncope, but the quality of the evidence supporting its use is poor. There are no randomized, placebo-controlled trials of fludrocortisone for the prevention of vasovagal syncope. In this 5-year study the investigators will test the hypothesis that fludrocortisone prevents recurrences of vasovagal syncope. 