Objective:To study the relationship of P wave dispersion (Pd),left atrial dimension(LAD) and atrial natriuretic peptide (ANP) between patients with paroxysmal atrial fibrillation and those with atrial premature beats. Methods:40 patients with paroxysmal atrial fibrillation(group A),50 patients with atrial premature beats(group B)and 50 healthy controls(group C) were included. The P wave maximal duration (Pmax) and the minimum duration(Pmin) and P wave dispersion(Pd=Pmax-Pmin)were measured using 12 leads electrocardiogram.Left atrial dimension(LAD)was measured by the echocardiogram and ANP was detected by radioimmunoassay(RIA) in each individule. Results:LAD,Pmax,Pd and ANP were higher significantly in patients with paroxysmal atrial fibrillation and atrial premature beats than those in healthy controls(P < 0.01);The significant difference also existed between patients with paroxysmal atrial fibrillation and those with atrial premature beats(P < 0.05);Pmax,Pd and ANP were all correlated with LAD(r=0.366,r=0.299,r=0.388,P < 0.01)and the best correlation was shown between Pmax and Pd(r=0.706,P < 0.01);Pmax and Pd had correlation with ANP (r=0.330,r=0.215,P < 0.01). Conclusion:LAD,Pmax,Pd and ANP are closely related to atrial arrhythmia.