Left bundle branch block (LBBB) is a common electrocardiographic (ECG) abnormality seen in patients whose normal cardiac conduction down both anterior and posterior left fascicles of the His-Purkinje system is compromised. Although LBBB is often associated with significant heart disease and is often the result of myocardial injury, strain or hypertrophy, it can also be seen in patients without any particular clinical disease. In isolation the presence of LBBB does not lend itself to any specific clinical concern, nor does it affect prognosis. However, in the proper clinical context, LBBB can of great consequence and importance, especially in patients presenting with acute chest pain, syncope and in those suffering from heart failure with reduced ejection fraction (HFrEF).