Sildenafil has been shown to be at least as effective as calcium channel blockers in treating severe Raynauds phenomenon (RP) associated with systemic sclerosis and digital ulceration. When given sildenafil for 4 weeks subjects had reduced mean frequency and duration of Raynaud attacks and a significantly lowered mean Raynauds condition score. The capillary blood flow velocity also increased in each individual patient and the mean capillary flow velocity of all patients increased significantly. These results came without significant reductions of the systemic blood pressure. However, the therapeutic effects of PDE5 inhibitors in primary (idiopathic) RP are less well defined.