Hyperthyroidism causes a variety of adverse effects on the cardiovascular system. Left ventricular (LV) asynchrony is defined as loss of the simultaneous peak contraction of corresponding cardiac segments. The aim of this study was to assess systolic asynchrony in patients with overt hyperthyroidism. Asynchrony was evaluated in 27 patients with overt hyperthyroidism and 21 controls. All the patients and controls were subjected to a tissue synchronization imaging (TSI). The time to regional peak systolic tissue velocity (Ts) in LV by the six-basal-six-mid-segmental model was measured on ejection phase TSI images and four TSI parameters of systolic asynchrony were computed. All TSI parameters of LV asynchrony increased in hyperthyroid patients compared to controls: the standard deviation (SD) of the 12 LV segments Ts (35.7 +/- 14.4 vs 20.1 +/- 10.1, P < 0.0001); the maximal difference in Ts between any 2 of the 12 LV segments (111.9 +/- 40.7 vs 65.9 +/- 30.7, P < 0.0001); the SD of the 6 basal LV segments (31.2 +/- 18.2 vs 16.8 +/- 9.7, P = 0.01); and the maximal difference in Ts between any 2 of the 6 basal LV segments (76.6 +/- 42.0 vs 44.4 +/- 25.7, P = 0.005). Patients with overt hyperthyroidism present evidence of LV asynchrony by TSI.