The typical sequence of mechanical and electrical events in LBBB on B-mode, M-mode and strain echocardiography. An early electrical activation of the septum results in a short initial septal contraction and causes the apex to move septally, whilst the septum moves leftward (yellow arrow in B-mode, red arrow in M-mode, and red strain curve). The delayed activation of the lateral wall pulls then the apex laterally during the ejection phase whilst stretching the septum (red arrow in B-mode and black in strain curve). This typical sequence of the septal-to-lateral apex motion is described as ‘apical rocking’. The septal inward motion is described as ‘septal flash’. Modified with permission from Stankovic I et al. Eur Heart J Cardiovasc Imaging. 2016; 17(3):262–9 (upper two panels).