The 80 year-old star was admitted to a San Diego hospital after arriving on a flight from New York. A spokesperson for the comic stressed that Lewis had, "a very minor heart attack".
The rep added that Lewis had been suffering from pneumonia, and that the star will recover quickly.
Jerry Lewis was best known in the 1950s as the side kick of actor Dean Martin. In 1996, he organised the Jerry Lewis telethon, which raised money for sick children in the United States.