what is a 2 day stress test

three month ago i had my stress test on the tredmill,was told everything was ok,now im waiting for my surgery date and they tell me i need to do stress test again because my heart rate wasnt high enough?what is this all about does anyone know? /

We greatly appreciate your interest in helping us build our Q&A database. To discourage vandals from posting garbage, however, we require people to register before posting.