Hello, I work in a hospital in a outpatient cardiac rehab program. Our protocol is give one nitro. SL and wait 5 min., along with some other protocols to follow, re-evaluate and if pt. still having CP, give another nitro SL. No more than 3 within 15 minutes. I instructed them for at home to do the same thing. However, if they are still having CP after the 3rd nitro. I tell them to call 911. And stress the importance of not driving themselves to the hospital. Maybe this is something that I should do some research on. We all know that EMS can provide that immediate treatment if needed, and time is of the essence. Thanks for making me think. Have a great day!