I STARTED MY 2006 MERCEDES-BENZ R350 AND ACTIVATED THE DRIVER SEAT WARMER ON HIGH. AFTER APPROXIMATELY 2.2 MILES INTO MY DRIVE (SPEED 30-45 MPH) MY SEAT FELT VERY HOT ON MY LOWER LEFT SIDE NEAR MY WAIST LINE. I REACHED BACK WHILE DRIVING TO FEEL HOW HOT THE SEAT WAS AND WAS SURPRISED BY A VERY HOT SENSATION AS THOUGH I HAD TOUCHED A HOT NEEDLE. AS I CONTINUED TO DRIVE AND PULL MY BODY FORWARD I NOTICED SMOKE RISING FROM BEHIND MY LEFT SHOULDER. I IMMEDIATELY PULL OVER ONTO A LEFT SIDE STREET AND PUT THE CAR IN PARK LEAVING IT RUNNING AND JUMPED OUT OF THE SEAT. THERE WAS A LARGE HOLE BURNED IN THE LEATHER AND IT WAS STILL SMOKING. I PATTED THE AREA DOWN WITH MY HAND TO NOTICE A GLOWING ORANGE SPARK AND IT CONTINUED TO SMOKE. I REACHED IN AND TURNED OFF THE HEATED SEAT BUTTON BY CYCLING IT THOUGH THE 2ND AND 3RD LEVELS. THE SEAT FINALLY STOPPED SMOKING. I LET THE HOLE IN THE SEAT COOL DOWN. CHECKING MY CLOTHING I REALIZED I HAD A HOLE AND SEVERAL MELTED SPOTS ON MY POLYESTER VEST I WAS WEARING. UPON COMING HOME I NOTICED ALSO A HOLE IN MY LIGHT COTTON SWEATER THAT WAS WORN UNDER THE VEST TWO DAYS PRIOR TO THIS INCIDENT I HAD FELT THE SEAT WAS HOT IN THE SAME AREA BUT THOUGHT MY SHIRT AT THE TIME WAS RAISED EXPOSING MY SKIN TO THE SEAT. *TR