To characterize the heartbeat-related distension of dissected and non-dissected thoracic aortic segments in chronic aortic dissection type b (CADB) ECG-gated computed tomography angiography was performed in ten CADB patients. For 20 time points of the R-R interval, multiplanar reformations were taken at non-dissected (A, B) and dissected (C) aorta: ascending aorta (A), aortic vertex (B), 10 cm distal to left subclavian (Ct, true channel; Cf, false channel). Relative amplitudes of aortic area and major and minor axis diameter changes were quantified. Area amplitudes were 12.9 +/- 3.7%, 11.4 +/- 1.8%, 16.5 +/- 5.9% and 10.5 +/- 5.7% at A, B, Ct and Cf, respectively. Area amplitudes were significantly greater at Ct than at Cf and B (p < 0.05). Major axis diameter amplitudes were 7.7 +/- 1.9%, 6.2 +/- 1.3%, 5.9 +/- 2.0% and 6.1 +/- 3.6% at A, B, Ct and Cf, respectively. There were no differences in major axis diameter amplitudes. Minor axis diameter amplitudes were 6.7 +/- 2.1%, 8.4 +/- 1.9%, 12.7 +/- 6.3% and 6.0 +/- 2.2% at A, B, Ct and Cf, respectively. Minor axis diameter amplitudes were significantly the greatest at Ct (p < 0.05). In CADB, the heartbeat-related distension of aortic area and diameter is evenly distributed over the non-dissected aortic arch. As a result from different blood flow properties, there are significantly greater conformational changes in the true channel of the dissected aorta.