If you are using those drugs, then you are doing a MPI/SPECT and are billing the correct codes. Those are the drugs normally injected for this type of nuclear medicine testing. From what information I could find on the MPI, even if rest is done the next day you can still only bill the one MPI cpt.
So basically, if it is standard protocol for the stress to be done on day 1 and day 2 is additional imaging for the rest portion, it is all included in the initial MPI code billed on day 1. If you have access to the CPT Assistant, look in May 2010 and Clinical Examples in Radiology, Winter 2010.
Hope I didn't confuse you too much, lol! Also, I am in the Wichita area

Have a great day!!