Stan Lee attends the Los Angeles premiere of 'Thor' held at the El Capitan Theatre in Hollywood, California - May 2, 2011. (Nikki Nelson/WENN.COM)

Comic book mogul Stan Lee has opened up about his recent health scare, revealing he underwent heart surgery last week.

The 90-year-old sparked concern among fans when he recently cancelled a number of personal appearances and he has now confirmed he was admitted to hospital in Los Angeles to have a pacemaker fitted.

Lee has released a statement to assure followers he is recovering well and jokingly compared his health problems to that of his comic book creation Iron Man.

He says, "Attention, Troops!... Your leader hath not deserted thee! In an effort to be more like my fellow Avenger, Tony Stark (Iron Man), I have had an electronic pacemaker placed near my heart to insure that I'll be able to lead thee for another 90 years.

"But fear thee not, my valiant warriors. I am in constant touch with our commanders in the field and victory shall soon be ours. Now I must end this dispatch and join my troops, for an army without a leader is like a day without a cameo!"