ANGLETON, Tex., Aug. 1 (AP) - Jurors heard testimony Monday from a pathologist who said the death of a man taking the painkiller Vioxx was more than likely caused by a heart attack, potentially damaging Merck's defense in the first liability case involving the drug to reach trial.

The videotaped testimony from Dr. Maria M. Araneta, a former assistant coroner for the Johnson County Medical Examiner's office near Fort Worth, was shown to the jury almost immediately after the Texas Supreme Court denied Merck's attempt to stop jurors from hearing it.

Dr. Araneta's autopsy report, which said that Robert Ernst, 59, died of an arrhythmia, or irregular heartbeat, secondary to clogged arteries. Merck says no studies show a link between taking Vioxx and a higher risk of arrhythmia.

In the deposition, though, Dr. Araneta said she thought Mr. Ernst's 2001 death from arrhythmia was more than likely caused by a heart attack.

Neither her report nor Mr. Ernst's death certificate identify a heart attack as the cause of death.

A Merck attorney, Joseph D. Piorkowski Jr., asked Dr. Araneta whether she was changing her conclusion in the autopsy report. "I'm not changing my opinion, I'm just explaining it further," she said. "That's the autopsy report, but it's not the end of the story."

The deposition by Dr. Araneta, now a pathologist in the United Arab Emirates, bolstered the plaintiff's contention that a heart attack was triggered by Mr. Ernst's arrhythmia but that he died too quickly for his heart to show damage.

Merck pulled Vioxx from the market in September after a study showed that it doubled the risk of heart attack if taken for 18 months of longer. Merck had fought to prevent jurors from hearing Dr. Araneta's testimony on the grounds that W. Mark Lanier, a lawyer for Mr. Ernst's family, failed to identify her by name as a witness by the pretrial deadline, which the company said violated court rules on surprise witnesses.

The 14th Court of Appeals, in Texas, denied the company's appeal of state District Judge Ben Hardin's decision that jurors could hear Dr. Araneta's testimony. The company then appealed to the state Supreme Court.