Abstract To demonstrate systolic and diastolic asynchrony in patients with left bundle branch block (LBBB), tissue Doppler imaging (TDI) of 4 different walls was performed in 27 normal controls, 29 patients with right ventricular pacing and normal left ventricular (LV) ejection fraction (EF; pacing LBBB), and 35 patients with idiopathic LBBB. Patients with idiopathic LBBB were further classified into those with LVEF >50% and those with LVEF <35%. Asynchrony was calculated as the coefficient of variation of the time intervals from the QRS complex to the peak systolic velocity and to the peak of early diastolic relaxation. Patients with pacing and idiopathic LBBB had significantly longer QRS durations (162 ± 20 vs 92 ± 7 ms, p <0.001) and larger systolic (15.9 ± 5.0% vs 4.1 ± 2.1%, p <0.001) and diastolic (3.7 ± 2.0% vs 1.4 ± 0.6%, p <0.001) asynchrony than controls. Those with idiopathic LBBB and low EF had significantly larger diastolic asynchrony (5.7 ± 2.1%) than those with pacing LBBB (2.9 ± 1.1%) and those with idiopathic LBBB and normal EF (2.0 ± 0.6%). Diastolic asynchrony was the only independent factor that correlated with LVEF (r = −0.64, p <0.001). Thus, idiopathic LBBB with LV dysfunction is characterized not only by systolic but also by diastolic asynchrony.