In order to evaluate atrial function after the restoration of normal sinus rhythm in patients with atrial fibrillation, an echocardiographic study was performed in 60 patients hospitalized for atrial fibrillation that was subsequently converted to sinus rhythm. The study population consisted of 60 patients, 41 males and 19 females, with a mean age of 67 ± 8 years. In etiological terms, 20 patients had atrial fibrillation with no associated pathology, 20 had an underlying ischemic cardiopathy an 20 had hypertension. The duration of atrial fibrillation varied from 24 h to 6 months. The restoration of sinus rhythm was spontaneous in 20 patients and drug induced in 40. Patients were divided into groups on the basis of the duration of the atrial fibrillation, the etiology of the atrial fibrillation and the size of the atrium. Transmitral Doppler inflow patterns at rest were assessed within 24 h after conversion to sinus rhythm, and 1 week, 1 month and 3 months later. The statistical significance of serial changes in peak A velocity and A wave integral was determined by analysis of variance. Using the peak A wave for atrial filling and the velocity-time integral as the index of atrial mechanical function, the following results were obtained: restoration of atrial mechanical function occurred earlier in hypertensive patients and in patients with atrial fibrillation only than in patients with associated ischemic cardiopathy. Restoration also occurred earlier in the group of patients that had atrial fibrillation for < 24 h and in patients whose left atrium was of normal size. Since the mechanical activity of the left atrium, evaluated as the peak A wave, does not necessarily return immediately after the restoration of sinus rhythm, a follow-up assessment of the contraction of the left atrium is appropriate.