This paper summarizes the results of the large-scale in vitro investigation of the interaction between wireless phones and cardiac pacemakers conducted by the Center for the Study of Wireless Electromagnetic Compatibility at the University of Oklahoma. The research focused on testing 29 pacemaker models with 5 different phone standards to (1) evaluate the amount of interaction between wireless phones and pacemakers, and (2) identify those factors which had a significant influence on the level of interaction. The phone standards included analog, CDMA, PCS 1900, TDMA-11 Hz, and TDMA-50 Hz. TDMA-50 Hz phones were operated in conjunction with a base station simulator in both ringing and talkback modes. Pacemakers included single-chamber and dual-chamber models tested in AAT,VVT and DDD modes. Tests were conducted with unipolar and bipolar lead configurations, and in the presence and absence of a simulated ECG signal. Relative orientation and coplanar separation distance of the phone and pacemaker were also considered.