Atrial fibrillation (AF) and congestive heart failure share several features and often coexist in the same patients; therefore, serial assessment of regional myocardial function is important for patients with AF. However, the clinical assessment of regional myocardial function in AF is unreliable and difficult because of beat-to-beat variation. Recent reports have shown that the ratio of the preceding to the prepreceding R-R interval (RR1/RR2) can be used to assess global left ventricular systolic function. Accordingly, we tested the hypothesis that regional wall motion can be estimated from a single beat based on RR1/RR2 in patients with AF. Peak systolic strain at basal, mid, and apical segments of the septal wall was measured by Doppler tissue imaging from an apical 4-chamber view for 30 seconds in 50 patients with AF (mean ejection fraction 52.1 +/- 15.3%; mean heart rate 76.4 +/- 16.0/min). There was a positive linear relationship between peak strain and RR1/RR2 and RR1, and a negative relationship with RR2, with the correlation of peak strain to RR1/RR2 was better than that in RR1 or RR2. Furthermore, peak strain at RR1/RR2 = 1 was calculated from the linear regression and compared with the average measured value of all recorded cardiac cycles in each patient. In all cases, average peak strain showed a significant positive correlation with RR1/RR2 at each segment (r = 0.99). In conclusion, regional myocardial strain at RR1/RR2 = 1 on the linear regression represents the average value of all recorded cardiac cycles in patients with AF.