Cardiac resynchronisation therapy (CRT) is indicated in refractory cardiac failure with electrical asynchrony defined by QRS complexes > or =120 ms duration. The search for mechanical asynchrony is proposed for better selection of patients for CRT. Ischaemic and non-ischaemic cardiomyopathy do not necessarily show the same form of asynchrony. The authors studied the differences in correlation between electrical and mechanical asynchrony in these two patient populations. Fifty patients (34 dilated non-ischaemic and 16 ischaemic cardiomyopathy) in NYHA Classes III and IV, LVEF < 35%, consecutively implanted for CRT in 2004, were included. The trans-thoracic echocardiography, the ECG and clinical parameters (NYHA, 6 minute walk test, VO2 max) were compared. A non-significant improvement of the correlation between the aortic pre-ejection time and QRS duration was observed in the non-ischaemic group (r = 0.78, p< 0.0001) compared with the ischaemic cardiomyopathy group ( r = 0.56, p = 0.019). Similarly, intraventricular asynchrony seemed to be correlated with the duration of QRS in the non-ischaemic group (r = 0.65, p < 0.0001) unlike the ischaemic cardiomyopathy group (ns). Sub-group analysis of patients with QRS durations < 150 ms and > or =150 ms showed an electromechanical correlation irrespective of the QRS duration in the non-ischaemic group but this was only observed with the aortic pre-ejection time with QRS > or =150 ms in the ischaemic group. The authors conclude that there is a significant correlation between electrical and mechanical asynchrony in patients with non-ischaemic cardiomyopathy. This correlation only applies to intraventricular asynchrony with QRS durations > or =150 ms in the ischaemic group. A decision for CRT requires echocardiographic evaluation in ischaemic cardiomyopathy.