A surface electrocardiogram (EKG) is emulated using signals detected by the internal leads of an implanted device. The emulation is performed using a matrix-based technique that separately emulates each of the individual signals of a multiple-lead EKG, rather than merely emulating a single combined EKG. In one example, each of the twelve signals of a standard 12-lead EKG are individually emulated, allowing for separate processing and display. The emulation technique takes into account factors affecting the relative locations of the internal leads, such as respiration and posture, to thereby provide a more accurate emulation. A calibration technique is provided for calibrating the EKG emulation for use with a particular patient and a verification technique is provided for automatically verifying the reliability of the emulation. Any significant loss in emulation reliability is likely caused by lead dislodgment and so automatic detection of possible lead dislodgment is also achieved.