NEW YORK (CNNMoney.com) - Jury selection began in Houston on Tuesday in the latest high-stakes legal battle for Merck ... and its first in a federal courtroom.

Evelyn Irvin Plunkett of St. Augustine, Fla., blames Vioxx, the company's withdrawn painkiller, for the 2001 death of her husband, Richard Irvin. This is the third Vioxx case in a list that exceeds 6,500 filed lawsuits.

This case holds great implications for the Whitehouse Station, N.J.-based drug giant, which enters the courtroom with one win and one loss beneath its belt. Both of Merck's previous battles were in state courts.

If Merck wins the Plunkett case, then it would allow the company to rack up another victory that "sends a message to [plaintiff] lawyers that they're not easy to win," possibly discouraging some cases from being brought to trial, said Frances Miller, law professor at Boston University.

But if Merck loses the Plunkett trial, then the company needs a change of fortune quickly before losing becomes a habit, said Miller.

"I wouldn't expect them to start settling if they lose this one," said Miller. "But if they lose 10 of them, yeah, I would think about settling."

Merck's Aug. 22 loss was in a small town in Texas near Houston, where the federal trial is now being held. The award in the case was $253 million, a figure likely to be reduced under state law. The company's Nov. 3 victory was in Atlantic City in its home state of New Jersey, where Merck fought off a plaintiff who had suffered a non-fatal heart attack.

In the Plunkett case, the plaintiff's husband died from a heart attack after taking Vioxx for about one month, according to plaintiff attorneys Jere Beasley and Andy Birchfield. Merck has insisted all along that Vioxx hasn't killed anybody.

Thousands of the lawsuits have been consolidated in federal court under Judge Eldon Fallon, who told reporters in May that the tally of federal cases could eventually reach 100,000. Houston is a temporary roost for Fallon and the federal Vioxx litigation, which was being coordinated in New Orleans until the city was paralyzed by Hurricane Katrina.

Vioxx was prescribed as an arthritis painkiller until Merck withdrew it from the market on Sept. 30, 2004 following a study that suggested there was an increase of heart attacks and strokes in patients who took the drug for at least 18 months. The loss of the drug eliminated $2.5 billion in annual revenue for Merck.

Fallon recently imposed a gag order on Merck and Plunkett and the lawyers representing them, so they couldn't comment directly on their strategies for the trial. But in previous trials, Merck's lawyers had argued that there was no evidence to back claims by patients taking the drug for less than 18 months that Vioxx caused their heart attacks. This defense failed in the Angleton, Texas, trial in August, but succeeded in Atlantic City.

Amid its Vioxx woes, Merck (Research) said Monday that it will cut 7,000 jobs and sell or close five factories to save up to $4 billion. Wall Street analysts, however, said the plan did not go far enough. Merck, America's second-largest drug maker behind Pfizer (down $0.14 to $20.96, Research), also faces a patent expiration in 2006 on its cholesterol drug Zocor, which totaled $5.2 billion in 2004 sales.

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