Study: Viagra Promising in Hypertension  NEW YORK (Reuters) - Viagra, Pfizer Inc's &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=PFE.N target=/stocks/quickinfo/fullquote"&gt;PFE.N&lt;/A&gt; famous  impotence treatment, demonstrated great promise in a late-stage  clinical trial for use in treating the often fatal disease  pulmonary arterial hypertension, researchers said.