ATLANTIC CITY, Oct. 31 - A Merck lawyer questioned the plaintiff's credibility in a closing argument Monday at the Vioxx personal injury trial here, saying that the drug had not caused the man's heart attack.

The lawyer, Diane Sullivan, told the panel of nine jurors, six women and three men, that the plaintiff, Frederick Humeston, 60, a postal worker from Idaho, had many risk factors that could have led him to suffer a heart attack in September 2001, which he survived. Those factors included Mr. Humeston's weight and his repeated clashes with his post office supervisors, Ms. Sullivan said.

"Mr. Humeston was really concerned that the post office was trying to remove him," she said.

Ms. Sullivan argued that Mr. Humeston had not proved that he actually took the painkiller Vioxx in the days or weeks leading up to his heart attack and that his explanation of the way he used the drug "doesn't add up."

Christopher Seeger, a lawyer for Mr. Humeston, will present his closing argument on Tuesday in the slow-moving civil case, which has entered its eighth week. A state judge, Carol Higbee, is overseeing the case, which is being heard in Atlantic County Superior Court, a few blocks from the casinos in this seaside town.

Investors, lawyers and executives at Merck are closely watching the trial, which comes less than three months after a jury in Texas ordered Merck to pay $253 million to the widow of a man who died of a heart attack in 2001 after taking Vioxx for eight months. Texas law will limit the award to no more than $26.2 million, and the company has promised an appeal.

Merck began selling Vioxx, particularly for arthritis pain, in 1999 and withdrew the drug from the market in September 2004 after a clinical trial showed that Vioxx increased the risk of heart attacks and strokes in subjects taking the drug for 18 months or more.

Merck faces lawsuits from almost 12,000 people who contend that they or their family members were hurt or killed by Vioxx. Lawyers for the plaintiffs say they have tens of thousands more cases, and Wall Street analysts say that if juries continue to return verdicts against Merck, it may eventually have to pay tens of billions of dollars to resolve the suits.

Ms. Sullivan spent part of her three-hour closing argument pursuing the point that Vioxx had never been shown to cause heart attacks with short-term use, and defending the company's decision to sell Vioxx despite some internal concerns about its risks. She also questioned Mr. Humeston's testimony, a potentially high-risk strategy.

Many plaintiffs' and defense lawyers say that jurors generally dislike watching corporations attack individuals, and if jurors decide that Merck is acting maliciously, they may punish the company by giving Mr. Humeston a large award. The verdict in Texas came after a lawyer for Merck conducted a tough cross-examination of Carol Ernst, the widow who brought the lawsuit.

But by making Mr. Humeston's testimony an issue, Ms. Sullivan has taken some of the jury's attention off internal Merck e-mail messages and documents that show that company scientists were concerned about Vioxx's heart risks before sales began. And jurors appeared to be paying close attention to Ms. Sullivan's argument that Mr. Humeston's testimony about his Vioxx use was implausible.

Mr. Humeston had chronic pain in his left knee because of an injury he suffered in the Vietnam War, and he took many different pain medications. In May 2001, almost four months before his heart attack, he filled a 30-pill prescription for Vioxx; in July, he filled a 20-pill prescription and received 6 sample pills from his doctor's office. Mr. Humeston had his heart attack on Sept. 18, 2001, well after he would have run out of Vioxx if he had used his prescriptions as soon as he filled them.

In his testimony, Mr. Humeston told jurors that he had indeed taken Vioxx in the days leading up to his heart attack. He said he took only two Vioxx doses in May before deciding that the drug did not work and saving the other pills. He then used both the May and July prescriptions after filling the July prescription, he said.

Ms. Sullivan said she found that explanation implausible. "Why do you get a new prescription of something you know doesn't work for you?" she said to the jury.

She also noted that an investigator for the post office had secretly videotaped Mr. Humeston in July 2001 to find out whether his knee injury had disabled him as much as he contended. On Sept. 17, 2001, a day before Mr. Humeston's heart attack, the inspector told Mr. Humeston's doctor that he believed Mr. Humeston could do additional work at the post office.

"Mr. Humeston's stress added up to a heart attack," Ms. Sullivan asserted.

After a break for lunch, Ms. Sullivan closed her argument by discussing several animal and clinical trials of Vioxx, which she said proved that Merck had not tried to hide the drug's heart risks. She ended on a more informal note, asking the jury not to punish Merck because it works to improve health and cure disease.

That drew a rebuke from Judge Higbee, who has clashed with Ms. Sullivan throughout the trial. After dismissing the jury, Judge Higbee told Ms. Sullivan that her appeal was inappropriate.

"For some reason," the judge said, "you just don't see where the line is."