Introduction: Intrinsic cardiac ganglionated plexi are known to modulate the autonomic interactions between extrinsic cardiac nerve activity (ECNA) and intrinsic cardiac nerve activity (ICNA). However, there are no quantitative data on the inter-relationship between ECNA and ICNA in ambulatory animals. Method: We implanted Data Sciences International (DSI) radiotransmitters in 5 dogs to record nerve activity (NA) from stellate ganglion (SGNA), vagus nerve (VNA), the ligament of Marshall (LOMNA) and the superior left ganglionated plexi (SLGPNA) simultaneously. Two different DSI radiotransmitters (DSI SNA beta for LOMNA, bandwidth up to 1000Hz, sampling rate up to 5KHz; DSI D70-EEE for SGNA, VNA and SLGPNA, bandwidth up to 100Hz and sampling rate up to 1KHz) were used for these recordings. Results: In randomly selected 1800 30-s segments (15 hrs), LOMNA and SLGPNA were detected in 7.5% (63 events) and 17.1% (154 events) of the 30-s windows, respectively. In 210 selected windows with LOMNA, the vast majority (94%) were associated with extrinsic cardiac autonomic nervous system discharges. In the remaining 6% of episodes, LOMNA activated alone without concomitant SGNA or VNA discharges. SLGPNA also showed a temporal association with the other nerve activities. Most of the SLGPNA were preceded by or co-activated with ECNA, including sympathovagal co-activation (139 windows, 90%), SGNA-only (13 windows, 8%) and VNA only (2 windows, 1%). We also noted that in 75 episodes (49%), the SLGPNA co-activated with LOMNA, whereas in 79 events (51%) the SLGPNA did not co-activated with LOMNA. Conclusions: Most ICNA showed a close temporal relationship with ECNA, indicating crosstalk between these two systems. A small number of ICNA activated without a temporal relationship with ECNA, suggesting that ICNA may activate alone without outside influence. These findings suggest that ICNA may be be independently arrhythmogenic.