Stress Cardiogram

I haven't done one of these for years. It's the kind where you are hooked up to an ecg machine and they take your readings while you are on a treadmill. They stopped it at 6 minutes. The cardiologist wants me to do another one but this time with some nuclear dye in my bloodstream. Apparently there might be a problem. Though he did saythat in 50% of the cases it turns out to be nothing. Then of course there's the other 50%...