Fragmentation of QRS (fQRS) complex is an easily evaluated non-invasive electrocardiographic parameter. Fragmentation of narrow QRS is defined as presence of an additional R wave (R′) or notching in the nadir of the S wave, or the presence of > 1 R′ in 2 contiguous leads, corresponding to a major coronary artery territory on the resting 12-lead ECG. Fragmentation of wide complex QRS consists of various RSR patterns, with more than 2 R waves (R′′) or more than 2 notches in the R wave, or more than 2 notches in the downstroke or upstroke of the S wave. Presence of fQRS has been associated with alternation of myocardial activation due to myocardial scar and myocardial fibrosis. Initial studies reported higher sensitivity of fQRS than Q wave for detecting myocardial scar and postulated that the presence of fQRS could be a good predictor of cardiac events among the patients with coronary artery disease. The presence of fQRS has been investigated among the patients with ischemic and non-ischemic cardiomyopathy suggesting that this ECG parameter may affect prognosis and risk of sudden cardiac death, risk of implantable cardioverter-defibrillator therapy and response to cardiac resynchronization therapy. In addition, there is evidence that fQRS could play an important role as screening and prognostic tool among the patients with Brugada syndrome, long QT syndrome, arrhythmogenic right ventricular dysplasia and cardiac sarcoidosis. This paper reviews definition, diagnostic and prognostic value of fQRS in different patient populations. (Cardiol J 2012; 19, 2: 114–121)