Atrial fibrillation (AF) despite the absence of heart failure is related to increased levels of natriuretic peptides (NPs). NPs have not been widely investigated in relation to left atrium (LA) function after sinus rhythm (SR) restoration and duration of AF. The aim of the study was to determine the changes of NPs levels and to define their relation with LA phasic function after electrical cardioversion (ECV). Methods. The study included 48 persistent AF patients with restored SR after ECV. NT-proANP and NT-proBNP were measured for all patients before the ECV. LA phasic function (reservoir, conduit, and pump phases) was assessed using echocardiographic volumetric analysis within the first 24 hours after ECV. Patients were repeatedly tested after 1 month in case of SR maintenance. Results. After 1 month, SR was maintained in 26 (54%) patients. For those patients, NT-proBNP decreased significantly (p=0.0001), whereas NT-proANP tended to decrease (p=0.13). Following 1 month after SR restoration, LA indexed volume decreased (p=0.0001) and all phases of LA function improved (p=<0.01). Patients with AF duration < 3 months had lower NT-proANP compared to patients with AF duration from 6 to 12 months (p = 0.005). Higher NT-proANP concentration before ECV was associated with lower LA reservoir function during the first day after SR restoration (R=-0.456, p=0.005), whereas higher NT-proBNP concentration after 1 month in SR was significantly related to lower LA reservoir function (R=-0.429, p=0.047). Conclusions. LA indexed volume, all phases of LA function, and NT-proBNP levels improved significantly following 1 month of SR restoration. Preliminary results suggest that higher baseline NT-proANP levels and higher NT-proBNP for patients with maintained SR for 1 month are related to lower LA reservoir function. The longer duration of persistent AF is associated with higher NT-proANP concentration.