Background: Atrial electrical activation time (aEAT) measured by signal average electrocardiography (SAECG) and mechanical activation time (aMAT) measured by Doppler tissue imaging (DTI) are known to be closely correlated in normal heart. However, it is not clear whether mechano-electrical relation can predict the long-term maintenance of sinus rhythm after electrical cardioversion (CV) for atrial fibrillation (AF). Methods and Results: Thirty patients with persistent AF were enrolled without taking anti-arrhythmic agents before CV. aMAT and aEAT was measured during maintenance of sinus rhythm after CV. The aMAT was determined as the time interval from initiation of the P-wave (lead II) deflection until the peak of the local lateral left atrial (LA) DTI signal in apical 4-chamber view. Atrial electrical activation time (aEAT) was defined as total P-wave duration using SAECG. During a mean follow up of 6 months, sinus rhythm was maintained in 15 patients (mean age, 50.2짹13.5 years) and AF was recurred in 15 patients (mean age, 54.8짹12.5 years). There were no significant differences in age, sex, blood pressure, B-type natriuretic peptide, pulse wave velocity, and routine echocardiographic parameters. There was strong correlation between aEAT and aMAT in patients who maintained sinus rhythm (R=0.609, p=0.047). In contrast, no correlation was found in patients with a relapse of AF (R=0.367, p=0.332). Conclusions: Compared to patients maintaining sinus rhythm after CV of AF, patients with relapse of AF did not have good correlation between aEAT and aMAT. This mechano-electrical mismatch might be one of the important factors for AF perpetuation.