"It's the first time, the very first time, we've ever shown that a diabetes drug can slow the progression of heart disease," Nissen said.
Nissens' study compared two commonly used diabetes drugs that work in different ways.
Amaryl causes the body to make more insulin, the hormone that lowers blood sugar. Actos makes the body more sensitive to the insulin it already has.
Patients taking both drugs lowered their blood sugar roughly the same, but those taking Amaryl had plaque buildup in the arteries of the heart - while those taking Actos had much better news.
"The group that got the insulin-sensitizing drug, Actos, they had no progression of coronary disease," Nissen said.
Doctors treating diabetes believe it's not just lowering blood sugar that's important in preventing heart disease.
"So, while I try and get my patients to have perfect blood sugars, I'm more concerned that their blood pressure is perfect, and that their cholesterol is lowered with a statin," said Dr. Stuart Weiss of New York University Medical Center.
"It's just not enough to know that the drug lowers blood sugar. We need to know 'what's it going to do for heart disease and the other serious complications that come with diabetes?," Nissen said.
This study was funded by the company that makes Actos. What remains to be seen now is whether this new information translates to fewer heart attacks and strokes.