Objective: The relationship between the autonomic nervous system (ANS) modulation of the sinus node and heart rate variability has been extensively investigated. The current study sought to evaluate, in an animal experimental model of pacing-induced tachycardia congestive heart failure (CHF), a possible ANS influence on the P wave duration and PR interval oscillations. Approach: Short-term (5 min) time and frequency domain analysis has been obtained in six dogs for the following electrocardiographic intervals: P wave duration (P), from the onset to peak of P wave (P p ), from the onset of P wave to the q onset (PR) and from the end of P wave to the onset of q wave (P e R). Direct vagal nerve activity (VNA), stellate ganglion nerve activity (SGNA) and electrocardiogram (ECG) intervals have been evaluated contextually by implantation of three bipolar recording leads. Main results: At the baseline, multiple regression analysis pointed out that VNA was strongly positively associated with the standard deviation of PP and P e R intervals (r 2 :0.997, p < 0.05). The same variable was also positively associated with high-frequency (HF) of P expressed in normalized units, of P p , and of P e R (b: 0.001) (r 2 : 0.993; p < 0.05). During CHF, most of the time and frequency domain variability significantly decreased from 20% to 50% in comparison to the baseline values (p < 0.05) and SGNA correlated inversely with the low frequency (LF) obtained from P e R (p < 0.05) and PR (p < 0.05) (r 2 :0.899, p < 0.05). LF components, expressed in absolute and normalized power, obtained from all studied intervals, were reduced significantly during CHF. Any difference between the RR and PP spectral components was observed. Significance: The data showed a significant relationship between ANS and atrial ECG variables, independent of the cycle duration. In particular, the oscillations were vagal mediated at the baseline, while sympathetic mediated during CHF. Whereas P wave variability might have a clinical utility in CHF management, it needs to be addressed in specific studies.