Objective The aim of the present study was to evaluate the presence and degree of spontaneous echo contrast (SEC) in the left atrium and of left atrial appendage (LAA) contractility before and after cardioversion (CV) in patients with recent-onset atrial fibrillation (AF). Methods Our study included 56 patients divided into two groups: group 1, comprising 32 clinically stable patients who were admitted to the Emergency Department with less than or equal to 48 h duration AF, and who underwent transoesophageal echocardiography (TEE)-guided CV; and the control group (group 2), comprising 24 patients admitted to the Cardiological Department for elective TEE-guided CV of greater than 48 h AF. All patients underwent repeat TEE within 1 h after successful CV. Results Patients with recent-onset AF (group 1) showed no thrombogenic milieu at baseline without any evidence of atrial stunning after successful CV. SEC mean grade (0-3 grading) was 0.09 +/- 0.3 versus 0.12 +/- 0.4 after CV (P=0.98), and LAA flow velocity was 60.7 +/- 19.4 versus 56.7 +/- 20.5 cm/s after CV (P=0.07). Group 2 patients showed a significantly higher degree of SEC compared with those in group 1 (0.09 +/- 0.3 vs. 0.66 +/- 0.7, P=0.0093) and significantly lower LAA flow velocities (60.7 +/- 19.4 vs. 32.5 +/- 12.4, P<0.0001), with significant worsening after successful CV (SEC degree: 0.66 +/- 0.9 vs. 1.37 +/- 0.9, P=0.0093; LAA flow velocity: 32.5 +/- 12.4 vs. 20.4 +/- 12.7 cm/s, P<0.0001). Conclusion The absence of thrombogenic milieu and of left atrial stunning after CV in patients with recent-onset AF favours early CV without anticoagulation, at least in patients with a low thromboembolic risk profile. These patients could be discharged earlier from urgent care. Copyright (C) 2017 Wolters Kluwer Health, Inc. All rights reserved.