Viagra, which treats a common but decidedly nonfatal male malady, might soon have a new role treating a rare but life-threatening disease that strikes mainly women. Doctors said yesterday that sildenafil citrate, the ingredient in Pfizer's impotence pill, had proven effective in a clinical trial as a treatment for pulmonary arterial hypertension - extremely high pressure in the artery carrying blood to the lungs. "It is a very promising new therapy for the treatment of a very severe disease," said H. Ardeschir Ghofrani, an assistant professor at the University of Giessen in Germany, who presented the results at the annual...