That's exactly what I was thinking, mike had a history of heart and chest problems in the past but the problem didn't become severe until his body went through multiple changes due to old age and stress(apparently). Your heart can only take so much and with Michael having the whole world on his shoulder, people suing him from left and right, slandering his name, the charges etc... you can only imagine the pain he was dealing with emotionally, physically and mentally. Mike didn't like his health issues to be discussed publicly, he wanted to remain strong for his family, friends and fans and he held up pretty well, yet realistically you knew something wasn't right with him constantly making those doctor visits. If there was a fragile/serious problem health wise with mike, why would his doctor's suggest him to perform? I wouldn't have gave him the ok on that, although it would have been nice to see him on that stage doing what he loved, if his health was at risk, that concert would have to be put on hold or not happen at all.