VANCOUVER - Two heart specialists told an inquiry into the use of Tasers on Tuesday that a jolt from the weapons can "almost certainly" cause heart problems and possibly even sudden cardiac arrest.

And a senior police officer who trains others on how to use the Taser said his training from the company that manufactures the device suggests the Taser does not lead to cardiac arrest.

Dr. Michael Janusz, a heart surgeon and professor of surgery at the University of British Columbia, told the inquiry that based on his study of available literature on Taser use, "almost all physicians would conclude that Tasers can induce ventricular fibrillation."

The hearing was told ventricular fibrillation is an extremely rapid rhythm in the heart's lower chambers, leading to ineffective contractions of the heart.

"In summary, Tasers almost certainly can cause cardiac arrest in humans, particularly in people with underlying heart disease," Janusz said.

A spokesman for Taser International has told the inquiry that Tasers are not risk free and that the term "non-lethal" does not mean safe.

Taser International has maintained there's a big difference between a Taser jolt causing death and contributing to death.

Staff Sgt. Joe Spindor, of the New Westminster Police Department, told the inquiry Tuesday his Taser training is based on what he was taught by Taser International.

"The information we receive is that it's safe to use on subjects," Spindor said.

He said he hadn't heard of Janusz's opinion on possible cardiac arrest.

"No. I've actually heard the opposite from Taser in my instruction."

Spindor said his officers don't get training in first aid or cardiopulmonary resuscitation.

But the officer also told the hearing he tells his students that a possible outcome of Taser use is injury or death.

Spindor said he teaches that the Taser can be used if a subject is displaying active resistance, though he conceded that the term is not written in his Taser policy.

Commission counsel Patrick McGowan asked if a person is being actively resistant if, after being advised he is under arrest, he starts to flee.

Spindor said that would be considered active resistance, as would behaviour an officer considered to be potentially dangerous or violent.

"The term active resistance isn't in our policy," he said, adding that the words should be added "to make it more clear."

The hearing also heard from Dr. Charles Kerr, another UBC professor and a heart surgeon, who said based on his reading of animal studies and the agitated state of most people who receive a Taser shock, he has concluded a Taser jolt could induce ventricular fibrillation.

"Whatever the cause of death in patients receiving Taser discharges, there does appear to be the potential of a cardiac arrest situation, as has been demonstrated on a number of occasions," Kerr said.

In a state of ventricular fibrillation, "the heart cannot pump blood and, unless it is interrupted quickly, sudden cardiac death will follow."

Kerr and Janusz agreed outside the inquiry that the Taser may still be preferable to a firearm or a club.

"My personal opinion is that they are probably better than a bullet," Kerr said.

But I think we need to have the understanding that. . . there is no question that there have been situations of sudden death," Kerr told reporters.

Janusz said each situation that a police officer uses a Taser has to be judged independently.

"Certainly in many or most situations it's a safer alternative than a gun or a club.

"But I believe the risks are there and you have to be cognitive of the risks and be prepared to deal with any consequence arising from it."

The current phase of the inquiry is looking at the use of the weapon in general and the next phase will look specifically at the death of Robert Dziekanski at the Vancouver airport last fall, after he was hit with an RCMP Taser.

The inquiry has heard that some police force policies use the term "active resistance" as a criteria Taser use.