What is best way to reheat the meat for Italian beef ?

I warm up leftover roast beef for French Dips by warming au jus and then submerging the meat for about 30 seconds, just to warm it. Place meat on roll and serve with warmed au jus or whatever juice you have from the Italian beef. The trick is not to keep it in the warm juice for too long, the meat will toughen up. Good luck! BB