Physical training modifies the sympathetic-vagal balance of autonomic nervous system. Previous studies have shown that such training also produces intrinsic modifications of cardiac electrophysiological properties in isolated heart during Ventricular Fibrillation (VF). Ten NZW trained rabbits were studied to test if the modifications are related to the activity of postganglionic parasympathetic neurons. Two records per subject were acquired during VF: before (G1) and after (G2) the infusion of atropine to inhibit the activity of neurons. Mapping records were obtained using a 240-channel electrode array located in the left ventricle of isolated heart (perfused by Langendorff system). VF was induced by stimulation at increasing frequencies. To analyze the time course of fibrillation, the records were processed in 4-second consecutive segments. For each channel and segment, the following parameters were computed: 1) Dominant Frequency (DF), obtained by the Welch periodogram b) Normalized Energy (NE) in a frequency band centered at the DF; c) Regularity Index (RI), which analyzes the similarity of local activation waves in every segment and channel; d) Coefficients of Variance of DF (CVDF), NE (CVNE) and RI (CVRI). For each segment, we obtained the average value of each of the parameters analyzed for all electrodes. The results are: a) DF (G1: 13.671 ± 0.509 Hz, G2: 14.783 ± 0.455 Hz), b) NE (G1: 0.398 ± 0.014; G2: 0.380 ± 0.013); c) RI (G1: 0.855 ± 0.017; G2: 0.865 ± 0.015), d) CVDF (G1: 0.109 ± 0.009; G2: 0.098 ± 0.008), e) CVNE (G1: 0.398 ± 0.014; G2: 0.380 ± 0.013 ) f) CVRI (G1: 0.084 ± 0.009; G2: 0.078 ± 0.008). None of these parameters showed significant differences between groups. Thus, the parasympathetic postganglionic neurons seem to have no effect on the cardiac response in VF due to physical training.