(CBS) As investigators study why a 14-year-old went into cardiac arrest after being hit with a Taser in Chicago, some new research raises questions on the Taser's safety.

As CBS News Correspondent Wyatt Andrews reports, the study, done by the Air Force and obtained by CBS News, found that repeated shocks from a Taser stun gun led to heart damage in pigs.

Specifically, the study examined the pigs' blood and found a jump in the enzyme Troponin T, the body's clearest sign of heart injury. It also found the pigs suffering high levels of blood acid, a potentially life threatening condition called acidosis.

"It's a red flag," says Dr. Charles Rackley, a respected cardiologist at Georgetown University Hospital.

CBS News showed the findings to Rackley.

Asked what his diagnosis would be if a patient came to him with these blood levels, Rackley says, "My initial impression would be that meant some heart muscle damage, or heart attack."

It should be noted the pigs in this study were shocked 18 times, when most people are hit once. And none of the pigs died. Still, Rackley believes blood levels like this in a human would be an emergency.

"The combination of the acidosis as well as the heart muscle damage would put this patient at high risk of developing ventricular fibrillation or sudden cardiac death," says Rackely.

Since 1999, there have been 86 deaths connected to the Taser and one-third of the deaths came from some kind of heart failure. Taser has never been blamed as the leading cause.

The Taser corporation declined an on camera interview but released a statement calling the Air Force's 18 shocks "extreme" and claiming the blood tests are similar to what "would be expected (from) strong physical exertion."

Taser also notes that the Air Force's researcher called his discovery of the Troponin T heart enzyme statistically insignificant. However, the physicians we contacted call the very existence of troponin T medically significant.

The finding raises new questions for a company that always said multiple Taser shocks make no difference. Now, here's evidence multiple shocks might injure the heart.

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