Which is the heatsheild you are refering to?
If you mean the one on the hood then you're ok, but since you said under the car i doubt that's it, so if you mean any under neath the car, I wouldn't want to drive to far until its replaced.
While you're replacing it, you should also consider replacing the plastic underpanels on the front of the bumper. They get old and tear our easy, and right now there's a group buy on them.
<span style='color:gray'><span style='font-family:Courier'>1995 e36 3 Series RIP
1999 e46 3 Series BURN IN HELL
2000 MR-S Roadster= Current</span></span>