P wave morphology has been shown to be modified in patients with paroxysmal atrial fibrillation (AF) and in healthy subjects of different age. These changes are commonly evaluated in the signal averaged ECG, thus in average P waves. Aim of this study is to assess beat-tobeat variations in P wave characteristics. Five-minute 12-lead ECG were recorded from 10 healthy subjects (C group), 10/10 patients with/without an AF recurrence (R/NR groups), after electrical cardioversion. Principal component analysis was performed on a beat-to-beat basis. The dynamic of the first three eigenvalues series and the beat-to-beat variability of the first three principal components (PCs) morphology were analyzed by calculating the distance between the average morphology over all the beats acquired and the morphology identified on each beat for the first three PCs. Most of the indexes were statistically different between C group and the patients with history of AF, highlighting higher regularity of the eigenvalues series as well as more similar PCs in healthy subjects. In addition, the series of the first eigenvalues was significantly less regular in R group compared NR group (Reg: 0.029 ± 0.020, 0.062 ± 0.033, p<0.05, R vs NR group).