KeyDown - graphic keeps moving!

I am writing a very simple Pong game - one bat each side and a ball. My problem is the bats keep moving long after I've taken my finger off the appropriate up/down key for each bat - and sometimes it takes a second or two for them to react to the up/down key press? I'll post the code if no-one can help but I'm sure this must be something very simple?

Thank you.

If Keydown(203) ;Left arrow
batX = batX - 1
End If

If Keydown(205) ;Right arrow
batX = batX + 1
End if

DrawImage bat,batX,batY

Something like that should do it, unless your keyboard is buggered?

Dabz