One third of patients meeting conventional electrocardiographic criteria for LBBB may be misdiagnosed and new ECG criteria for LBBB have been proposed (Strauss's criteria). We used 2D speckle tracking echocardiography (2DSTE), to compare LV mechanics in LBBB with conventional versus Strauss's criteria.We studied 49 asymptomatic patients with LBBB: 16 with conventional (mean age 69 years, 56% were men) and 33 with Strauss's criteria (mean age 66 years, 61% were men), LVEF>45%, and no significant obstructive CAD. 3D echo was performed to measure LV end diastolic (LVEDV) and end systolic (LVESV) volumes, sphericity index (SpI), LV remodelling index (LVRI) and LVEF. 2DSTE was used to measure parameters of LV dyssynchrony: septal to posterior wall time to peak radial strain (SW-PW delay), longitudinal strain delay index (L-SDI), longitudinal strain rate dispersion index (L-SRDI) and LV mechanical dispersion (LVMD). We also measured LV cardiac work indices: global work efficiency (GWE), global work index (GWI), global constructive work (GCW), and global wasted work (GWW).L-SDI was significantly higher in patients with Strauss's criteria than in conventional one (3717% vs 2510%, respectively, p = 0.007). GWW tended to be higher in patients with Strauss's criteria than in conventional one (325132% vs 267124% respectively, p = 0.079).LVESV index was positively correlated with GWW (p= 0.001). So, Patients in whom LBBB was diagnosed according to Strauss's criteria showed significantly higher intraventricular dyssynchrony and tendency for higher LV wasted work than patients with LBBB according to conventional criteria.