A medical device locating system for determining disposition of a sensor coil in a subject, said system comprising: a. an array of three or more triplet drive coil sets arranged in a block which is configured to be placed on a patient's chest, each drive coil set including at least three discrete drive coils (38, 40, 42), each of the discrete drive coils being electromagnetic coils; b. at least one sensor coil adapted to provide one or more sensor coil response signals; c. a first system component configured to provide AC drive signals energizing said discrete drive coils, wherein the provision of drive signals includes one or both: (i) sequentially driving one or a pair or a triplet of said discrete drive coils within a triplet drive coil set; and (ii) selectively providing phase inversion of the drive signal to any one, two or three of said discrete drive coils within a triplet drive coil set; d. a second system component for measuring resulting one or more sensor coil response signals, including one or more of sequential single, paired or triplet sensor coil response signals; e. an electrocardiogram operably associated with said triplet drive coil array wherein one or more ECG reference leads are configured to be placed on said subject and a ECG signal lead is provided by a conductive core wire supporting said sensor coil; and f. a computing component configured to calculate sensor coil disposition in the subject relative to said triplet drive coil sets, characterized in that the system further comprises: g. a display configured to show the disposition of said sensor coil in said subject relative to the array of said triplet drive coil sets in combination with the ECG signal of the subject over time, wherein said display is configured to display a P-wave or other wave changes of the ECG of the subject in combination with the disposition of said sensor coil and wherein the computing component is further configured to use a waveform analysis to assist a user in recognizing changes occurring to the P-wave of the ECG or wave elements of the ECG signal, the system further comprising one or more of a catheter, a guide wire and a stylet with said sensor coil being disposed in physical association therewith, and further comprising an integrated conductive ECG lead associated with the sensor coil, the conductive ECG lead providing an electrical ECG signal, wherein the display is configured to display the P-wave changes or other waveform changes so as to indicate a proximity of the catheter, stylet or guide wire relative to the heart of the subject. a. an array of three or more triplet drive coil sets arranged in a block which is configured to be placed on a patient's chest, each drive coil set including at least three discrete drive coils (38, 40, 42), each of the discrete drive coils being electromagnetic coils; b. at least one sensor coil adapted to provide one or more sensor coil response signals; c. a first system component configured to provide AC drive signals energizing said discrete drive coils, wherein the provision of drive signals includes one or both: (i) sequentially driving one or a pair or a triplet of said discrete drive coils within a triplet drive coil set; and (ii) selectively providing phase inversion of the drive signal to any one, two or three of said discrete drive coils within a triplet drive coil set; (i) sequentially driving one or a pair or a triplet of said discrete drive coils within a triplet drive coil set; and (ii) selectively providing phase inversion of the drive signal to any one, two or three of said discrete drive coils within a triplet drive coil set; d. a second system component for measuring resulting one or more sensor coil response signals, including one or more of sequential single, paired or triplet sensor coil response signals; e. an electrocardiogram operably associated with said triplet drive coil array wherein one or more ECG reference leads are configured to be placed on said subject and a ECG signal lead is provided by a conductive core wire supporting said sensor coil; and f. a computing component configured to calculate sensor coil disposition in the subject relative to said triplet drive coil sets, characterized in that the system further comprises: g. a display configured to show the disposition of said sensor coil in said subject relative to the array of said triplet drive coil sets in combination with the ECG signal of the subject over time, wherein said display is configured to display a P-wave or other wave changes of the ECG of the subject in combination with the disposition of said sensor coil and wherein the computing component is further configured to use a waveform analysis to assist a user in recognizing changes occurring to the P-wave of the ECG or wave elements of the ECG signal, the system further comprising one or more of a catheter, a guide wire and a stylet with said sensor coil being disposed in physical association therewith, and further comprising an integrated conductive ECG lead associated with the sensor coil, the conductive ECG lead providing an electrical ECG signal, wherein the display is configured to display the P-wave changes or other waveform changes so as to indicate a proximity of the catheter, stylet or guide wire relative to the heart of the subject.