Kevin Federline -- Rushed to Hospital After Heart Scare

Kevin Federline was rushed to the hospital after his heart showed signs of distress.

The pic shows Kevin wearing an oxygen mask earlier today in Australia, where he was shooting a reality show, "Excess Baggage."

Federline -- who is 33 years old and significantly overweight -- was playing football with an Australian rules football team when he fell ill. K-Fed, who is 6', weighs 231 lbs.

We're told he spent the night in the hospital for observation.