TMZ spoke with Randy's brother, Lanny Poffo, who tells us the wrestling legend suffered a heart attack while he was behind the wheel around 9:25 AM ... and lost control of his vehicle.
Earlier this month, Savage celebrated his 1-year anniversary with his new wife Lynn.
Savage was 58.
Macho Man began wrestling in the WWF in 1985 and became a superstar with his trademark catchphrase "Ooooooh Yeaahhhhh." Savage was so popular, he became the spokesperson for Slim Jim in the mid '90s ... and became virtually synonymous with the brand.
UPDATE: Florida Highway Patrol tells TMZ ... Savage was driving his 2009 Jeep Wrangler when he veered across a concrete median ... through oncoming traffic ... and "collided head-on with a tree."
Savage was transported to Largo Medical center, where he died from his injuries.
Savage's wife was a passenger in the vehicle during the collision -- but survived with "minor injuries." She was transported to a different local hospital where she was treated.
According to officials, Randy and Lynn were both wearing their seatbelts at the time of the accident.
Cops say alcohol was NOT a factor.
An investigation into the accident is underway.