Fish oil supplements touted as important weapons in the fight against heart disease may not actually be what the doctor ordered.

According to a new study, the little golden capsules may actually do more harm than good in patients who have unstable heart rhythms.

For the purposes of their study, doctors focused on 200 people -- all of whom suffered from erratic heartbeats, and had defibrillators implanted in their hearts.

The purpose of the tiny device is to shock the heart back into rhythm, whenever it beats out of control.

Researchers thought the fish oil supplements would help to regulate the test subjects' heartbeats, but the opposite happened.

Among the control group who were given only olive oil supplements, 36 per cent had dangerous episodes over a six-month period.

Among those who took the fish oil supplement, however, that number nearly doubled. Two-thirds had episodes of the rapid or unstable cardiac rhythm that often signals a heart attack.

For the researchers conducting the study, the conclusion was an unexpected one.

"We were certainly surprised by the result," study author Dr. Merritt Raitt of the Oregon Health and Science University told CTV News. "We honestly had expected to see a reduction in the risk of these dangerous rhythms in patients that took fish oil."

What the researchers did see, however, may mean a change in medical advice for the estimated 30,000 Canadians who live with the surgically implantable defibrillators.

Dr. Paul Dorian of Toronto's St. Michael's Hospital is already considering a new approach.

"Right now what I will tell patients if they have a defibrillator is that there is no good evidence that it is beneficial and that it may be harmful and I'm not really keen on it."

Previous research has shown that fish oil supplements, with their intense concentration of omega-3 polyunsaturated fatty acids, can reduce the risk of fatal heart attacks by 25 per cent in those who've already suffered a previous attack.

Published research has also shown that fish oil can be used to treat a variety of conditions including asthma, arthritis, and colitis, as well as lupus, cystic fibrosis and schizophrenia.

With a report from CTV Health Specialist Avis Favaro