Celebrex Trial Halted After Heart Attacks  NEW YORK (Reuters) - A government-sponsored trial of 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; blockbuster arthritis drug Celebrex was halted  after patients taking the medicine had more than twice as many  heart attacks as patients taking a placebo, the company said on  Friday.