Letang, 26, reported dizziness and nausea last week and an examination determined he had a small hole in his heart, a common condition he had since birth, that could have caused the stroke.
The team said the condition is "treatable with blood thinners and at this point is not believed to be career-threatening."
Letang is to be re-evaluated after receiving treatment for six weeks.
"I hope that by making my condition public at this time, I can help other people by encouraging them to seek medical help if they experience some of the symptoms associated with a stroke -- regardless of their age or general health," Letang said in a statement. "It obviously was a shock to get the news but I'm optimistic that I can overcome this and get back on the ice."
Letang has 10 goals and eight assists in 34 games this season. He's played his entire seven-season NHL career with the Penguins.