Since the Food and Drug Administration first issued a warning that grain-free dog foods may cause heart damage to pets, more than 200 dogs have died from the condition.

According to NBC News, scientists are still trying to find the actual connection and cause why grain-free foods cause potentially fatal canine dilated cardiomyopathy or DCM. They believe the source may be the ingredients dog food manufacturers have included in their products to replace the grains.

“Most of the diets associated with the reports of non-hereditary DCM have legume seed ingredients, also called pulses,” said FDA spokesperson Monique Richards. She added that foods such as peas and lentils were often in the ingredients list.

Some experts point to the low levels of taurine in some of the affected dogs’ blood. Taurine is an amino acid required for the development and function of the heart muscle cells, according to Texas A&M University. Some speculate that the legumes in grain-free food may interfere with the dog’s ability to make taurine or perhaps absorb it.

A recent study found that dogs with DCM who were consuming non-traditional foods improved and lived longer when they switched to a more traditional canine diet and supplemented with heart medication, according to NBC News.

Dr. Lisa Freeman, with the Cummings School of Veterinary Medicine at Tufts University, said that the hearts of dogs with DCM increase in size and the contractions become weaker. But when the affected dogs are fed food that contains grains, their condition often improves and they may live longer.

The Pet Food Institute said they are currently investigating the link between diet and potentially deadly DCM. Meanwhile, experts say that dog owners should discuss the best diet for their pets with their veterinarians based on their health and medical history.