Scientists at the University of Calgary have made a discovery they believe could one day help in the battle against heart disease, which is the second leading cause of death in Canada.

A team of researchers identified a new immune cell with healing properties in a sac surrounding the hearts of both mice and humans.

The study — published in the journal Immunity — reveals researchers first discovered the cell in mice with damaged hearts.

"We've actually found immune cells that live in this area and play [a] beneficial role in helping the heart heal after injury," said the study's lead author and University of Calgary post-doctoral fellow Justin Deniset.

By injecting an extra gene into the mice, scientists triggered a change in the cells, making them appear flourescent green. They were able to track the cells using a sophisticated microscope and watched as these bright green illuminated spots surrounded the heart during a heart attack.

Researchers say this slide shows immune cells, pictured in fluorescent green, surrounding damage in the heart. (University of Calgary)

"[These cells] actually helped to reduce scarring and help the heart function more," he said.

That's important, according to Deniset, because hearts have a limited ability to repair themselves. After a heart attack scar tissue forms, stopping the heart from beating properly and eventually leading to heart failure.

"We think this has been missed," said Dr. Paul Kubes, director of the Snyder Institute for Chronic Diseases at the Unviersity of Calgary and one of the study's authors.

"No one's really gone in there and really explored the different kinds of immune cells."

Cells routinely discarded during surgery

Researchers quickly discovered people have these immune cells in the fluid around their hearts too.

But the cells are literally being thrown away during open heart surgery — suctioned out as surgeons cut their way through the pericardium— the sac surrounding the heart — to the heart itself.

"Unfortunately because we never thought this fluid did anything, we just suck it away … and it goes straight to the garbage," said Dr. Paul Fedak, cardiac surgeon and incoming director of the Libin Cardiovascular Institute of Alberta at the University of Calgary.

Dr. Paul Fedak, a cardiac surgeon and one of the study's authors, says the discovery of these cells could lead to new therapies and hope for people suffering from heart disease. (Audrey Neveu/Radio-Canada)

Now, doctors and scientists are rethinking that practice.

"Maybe that fluid needs to be there. Maybe we need to be restoring that fluid. Maybe we should be getting these cells and amplifying their response so … we've got a new avenue for potential therapies."

According to Fedak the next phase of research has already begun. Scientists are now taking fluid samples from patients with different kinds of heart disease to investigate how the cells work in people.

"I'm really excited about this because I think it opens a new door for potential therapies," said Fedak who sees patients with heart disease every day.

"Can we take these cells, can we expand them, can we increase their number, can we reinject them into that space or directly into the heart to help repair hearts after injury? It's entirely possible."