This lecture reviews electrophysiological techniques that are currently available for assessing ventricular dyssynchrony in patients. The most commonly used, but also least informative, approach is measuring QRS duration from the 12-lead ECG. Considerably more informative is the area under the QRS complex. This can be obtained by converting the 12-lead ECG to vectorcardiogram (VCG). QRSarea is a strong predictor of response to cardiac resynchronization therapy (CRT). More advanced methods use multiple chest electrodes, such as the “ECG-Belt” that consists of two bands with a total of 53 electrodes around the chest and ECG-imaging where >100 electrodes are used in combination with anatomical information of heart and chest using CT or MRI images. These techniques provide a standard deviation of activation times (SDAT) to express the degree of dyssynchrony. Besides, ECG-imaging also creates 3D maps of activation. The UHF-ECG technique may be positioned in between the VCG and the ECG-Belt. It does not require cardiac imaging and uses the 12 or 14 lead ECG, from which it calculates several variables, such as electrical dyssynchrony (e-DYS) and duration of local depolarization (Vd). The former may be compared with “ventricular electrical uncoupling” (VEU) derived from ECG-imaging. Vd is unique for UHF-ECG and reflects the contribution of the rapid conduction system underneath the various precordial leads. The results can also be displayed in maps of electrical activation in a lay-out comparable to linear M-mode in echocardiography. The fact that normal ECG recording suffices using only a better (higher frequency sampling) amplifier may make this technique an interesting alternative way to assess ventricular dyssynchrony in patients with pacemakers.