 Papaverine, a nonselective phosphodiesterase inhibitor, is beneficial and selectively used for treatment of active vasospasm. Its use is limited by its short duration of action, and its nonspecific nature results in systemic vasodilation and subsequent hypotension. Sildenafil citrate, a selective PDE-V inhibitor, has been shown to enhance the reactivity of the cerebral vasculature in normal healthy adults and has been shown to decrease the severity of vasospasm in animals with experimentally induced SAH. These effects have been noted with minimal effects on systemic hemodynamics. Given that sildenafil citrate has safely demonstrated the expected clinical effect of cerebral arterial dilation in normal healthy humans as well as animals with and without induced SAH, the aim of this study is to determine if this medicine shows efficacy in humans with SAH secondary to ruptured aneurysm. 