Ultrasonic tissue characterization has the potential to provide quantitative information which could characterize the functional and structural state of cardiac muscle. In this study we aimed to determine whether the integrated backscatter is measurable and quantifiable in left atrial posterior walls in patients with chronic atrial fibrillation (AF) and can be used to identify changes in atrial structure and contractility. In 26 patients with chronic atrial fibrillation and 20 patients in sinus rhythm (SR), integrated backscatter signal (IBS) was analyzed by acoustic densitometry. Real time IBS was measured from the parasternal long axis view of the left atrial posterior walls. Cyclic variation of IBS (CVIB) was expressed as the difference between end-diastolic (peak) and end-systolic (nadir) IBS values averaged over all cardiac cycles. CVIB values obtained from left atrial posterior wall in atrial fibrillation group were statistically different from control group (P < 0.05). IBS of the left atrial posterior wall indexed by pericardium (IBS%) were higher in patients with AF than in patients with SR (P < 0.05). CVIB and mean IBS values which were obtained with IBS method may be useful to determine myocardial contractile performance and myocardial structural properties, respectively. IBS of the LA posterior wall indexed by pericardium provides an objective quantitative measure of atrial fibrosis.