Robin Williams' 2009 open-heart surgery could have contributed to the late star's demise, possibly serving as a trigger to the comedian's downward spiral to severe depression.
Five years ago, the Oscar-winning actor underwent surgery at the Cleveland Clinic to replace his aortic valve, fix his mitral valve and correct an irregular heartbeat.
Depression is one side effect of cardiac surgery.
It's unknown exactly when Williams' battle with depression began, but his rep issued a statement after the star's death on Monday at 63, noting he had "been battling severe depression of late."
"Open-heart surgery has historically been known to affect a person's cognitive functioning following recovery," Dr. Jeffrey Lieberman, chief of psychiatry at New York-Presbyterian Hospital Columbia, told the Daily News.
"The valve replacement involves stopping the heart while you're replacing it, and having that kind of procedure with general anesthesia, there is an increased frequency of depression occurring in the aftermath," he said.
A number of factors could contribute to this post-operative depression, said Dr. Tara Narula, associate director of the cardiac care unit at Lenox Hill Hospital and a spokeswoman for the American Heart Association and American Stroke Association.