WASHINGTON (Reuters) - A quick shock from a Taser may have zapped a man’s fluttering heart back into a healthy rhythm, doctors reported on Tuesday.

They cited the incident as evidence that the devices, which are used by police who want to use less-than-deadly force to incapacitate people but are condemned by some civil rights groups as dangerous, may affect the heart as critics allege.

In this case, the outcome was a happy one, the doctors reported in the Annals of Emergency Medicine. Several lawsuits in the United States and Canada contend the devices, which use an electric charge to subdue an attacker, can stop the heart.

The 28-year-old patient was fleeing police and jumped into a lake in April, when the water was still very cold.

“I don’t know exactly what he had done but he fled capture from them and he hid in a lake,” said Dr. Kyle Richards, a cardiologist at Hartford Hospital in Connecticut, who treated the man when he was taken to an emergency room.

Richards said the patient was experiencing an irregular heart rhythm known as atrial fibrillation, possibly as a result of the cold and shock.

After treatment, the patient was eager to leave. “He got very combative and started yelling in my face and that’s when I left the room and got security,” Richards said.

Police and security used a Taser stun gun, which shoots out a lead connected to two barbs that can deliver up to 50,000 volts. They used a low-voltage charge meant to cause pain rather than a longer, higher-voltage jolt meant to incapacitate.

The patient calmed down and another electrocardiogram showed his heart rhythm was normal.

“This is the first report of a patient receiving a shock of this kind and having a positive outcome,” Richards said.

Amnesty International says that since 2001 more than 290 people have died in North America in incidents involving the weapon. Taser International says there is no evidence the gun directly caused the deaths.

Richards said studies done in pigs show the weapon can affect the heart muscle.

This case provided a controlled situation, with almost continuous monitoring of the patient’s heart.

Richards noted that the patient was not hooked up to the electrocardiogram at the precise moment of being shocked.

“People can spontaneously go from atrial fibrillation into a normal rhythm without any intervention at all. You cannot conclusively say that the Taser did it,” he said. But he said he believed it did.

“It’s just one more thing that says, hey, Tasers can actually affect the heart.”