Viagra, Pfizer Inc’s famous impotence treatment, demonstrated promise in a late-stage clinical trial for use in treating the often-fatal disease pulmonary arterial hypertension.

In data presented on Wednesday at the American College of Chest Physicians annual meeting in Seattle, Viagra after 12 weeks improved the exercise capacity of patients as measured by distance covered in a 6-minute walk.

Pulmonary arterial hypertension (PAH) is a dangerous build-up of blood pressure in arteries that connect the heart to the lungs.

The 278-patient study tested Viagra, also know by its chemical name sildenafil citrate, at 20, 40 and 80 milligrams taken three times daily versus a placebo.

The Viagra patients at each dose fared better than the placebo group in the 6-minute walk test, researchers said.

The erectile dysfunction drug was originally designed to treat the heart condition angina, which did not work out, when researchers stumbled upon the effect that became its multibillion-dollar use.

As Viagra faced increasing competition in the erectile dysfunction arena, Pfizer stepped up its research into other potential uses for the drug, including in pulmonary arterial hypertension.

The Viagra PAH data was being closely watched by Actelion and its investors as an approval for Viagra to treat PAH would provide direct competition for Actelion’s flagship drug Tracleer, which accounts for virtually all of the Swiss biotechnology company’s revenue.

Tracleer is currently the only approved oral treatment for PAH.

Encysive Pharmaceuticals is also developing an experimental PAH treatment called Thelin.