A state court judge in Los Angeles has declared two mistrials after a jury failed to return verdicts in cases filed by two plaintiffs who alleged Merck's ( MRK) Vioxx contributed to their heart attacks.

Lawrence Appell of Scottsdale, Ariz., said he used Vioxx for 18 months before suffering a heart attack, at age 51, on Dec. 23, 2000. He continued to use Vioxx until September 2004.

The other plaintiff, Rudolph Arrigale of Westminster, Calif., said he used the painkiller for 4 1/2 months before his heart attack at age 72 on March 18, 2002.

"Both plaintiffs failed to prove their case," said Thomas Yoo of the law firm Reed Smith, a member of the Merck defense team. "We are fully prepared to defend these cases if they are tried again."

Merck is facing thousands of lawsuits by plaintiffs who have alleged Vioxx caused a variety of health problems. The company pulled the drug off the market in September 2004.