PALM CITY, Fla. -- The FDA is investigating a potential dietary link between canine dilated cardiomyopathy (DCM) and dogs eating certain grain-free dog foods.

The foods of concern are those containing legumes such as peas or lentils, other legume seeds, or potatoes listed as primary ingredients.

That is information Floyd's owners wish they would have known. He's an 11-year-old Staffordshire terrier .

A few weeks ago, something terrible happened, when they took him out for a walk.

Laila Esmaeel says, "We saw his legs give out and he just fell over. Hit the ground like a ton of bricks."

Her boyfriend Russell Taylor described it like this: "I thought he was having a seizure."

The next day Russell and Laila's vet broke the news, Floyd had dilated cardiomyopathy which causes an enlarged heart.

Dr. Annette Sysel at Martin Downs Animal Hospital in Palm City, says if DCM is not caught early, it can be fatal. She is currently treating two dogs with DCM.

She says the FDA has been studying the potential link between canine heart disease and diet since 2014.

And in June of this year, issued a warning about certain brands of grain free pet food and their possible connection to dilated cardiomyopathy.

“So is there a direct link? Dr. Sysel was asked. She says, "No, but when you look at all cases of DCM, especially in breeds of dogs not predisposed to the condition, a lot of those dogs, 90%, are on grain-free diets."

Just walk down any pet food aisle and it's clear grain free is the hot new trend. It's caught on much like gluten free did in people food.

Some well-intentioned owners may think it's better for their pets. Dr. Sysel explains, "Grain free does not mean gluten free, carb free--it just means certain grains are eliminated from the diet."

Vets say dogs with allergies and gastrointestinal issues often need to go on a grain-free diet.

Floyd was one of them. In fact, the food he was eating is one of the 16 brands on the FDA warning list. Laila told me they had no idea Floyd's food could make him so sick. A quick Google search made her realize they weren't alone. "I found hundreds of reports from the FDA from other pet owners whose dogs had very similar symptoms and instances such as the fainting episode."

Dr. Sysel says, exercise intolerance, tiring easily, lethargy, and weakness are other signs to look for in your pet. "If we're worried, then the next step is a cardiac ultrasound to determine any changes to the heart."

Today Floyd is doing well. He's off the grain-free food and responding to heart medicine. Leila says: "I don't want to start crying. He's just great. He’s been our little guy, our best friend for all these years."

If you are confused about what to feed your dog, Dr. Sysel says to talk to your vet. Avoid feeding your dog what's trendy and buy from a well-known pet food company.

Pet owners and veterinarians are urged to report all cases of DCM to the FDA.

RELATED: How to report a pet food complaint

Cats can get dilated cardiomyopathy too, but not to the degree that dogs do.