Was he a smoker?
https://www.cbc.ca/sports/hockey/nhl/guy-lafleur-obituary-1.5766441
The cause of death was not immediately known. However, Lafleur suffered through health issues in the latter stages of his life. In September 2019, he underwent quadruple bypass heart surgery, which was followed by lung surgery two months later.
Then, in October of 2020, he endured a recurrence of lung cancer.