Background: Atrial remodelling has been poorly investigated in atrial fibrillation (AF), and few studies have focused on biatrial remodelling. Aim: To evaluate right atrial (RA) and left atrial (LA) remodelling in AF using global atrial reservoir strain and three-dimensional (3D) atrial volumes, according to rhythm outcome at mid-term follow-up. Methods: Two-dimensional and 3D transthoracic echocardiography (TTE) were performed within 24hours after admission (M0) and at 6-month follow-up (M6) in patients admitted for AF. RA and LA variables were assessed: body surface area-indexed maximum 3D volume (Max 3D RA Voli, Max 3D LA Voli) and minimum 3D volume (Min 3D RA Voli, Min 3D LA Voli); atrial emptying fraction (3D RAEF, 3D LAEF); atrial expansion index (3D RAEI, 3D LAEI); and global RA and LA reservoir strain. Results: Forty-eight consecutive patients were included prospectively. Three groups were identified depending on rhythm at M0 and M6: AF at M0 and sinus rhythm (SR) at M6 (AF-SR) in 25 (52.1%) patients; AF at M0 and AF at M6 (AF-AF) in 13 (27.1%) patients; and SR at M0 (spontaneous cardioversion before first TTE) and SR at M6 (SR-SR) in 10 (20.8%) patients. Between M0 and M6 in the AF-SR group, we found: significant decreases in Max 3D RA Voli (P=0.020), Min 3D RA Voli (P=0.0008), Max 3D LA Voli (P=0.001) and Min 3D LA Voli (P=0.0021); significant increases in 3D RAEF (P=0.037) and 3D RAEI (P=0.034); no significant differences in 3D LAEF and 3D LAEI; and significant increases in global RA and LA reservoir strain (both P<0.0001). There was no significant difference with regard to these variables in the AF-AF and SR-SR groups. Conclusion: 3D volume and strain analyses were useful in the evaluation of RA and LA reverse remodelling in successfully cardioverted patients with AF.