BACKGROUND: Real-time three-dimensional echocardiography (RT3DE) is an alternative modality to tissue Doppler imaging (TDI) for assessment of intraventricular dyssynchrony but its role is yet to be defined. OBJECTIVES: To (1) compare RT3DE and TDI for assessment of intraventricular dyssynchrony; (2) determine whether the two techniques agreed regarding the magnitude of dyssynchrony and identification of the site of maximal mechanical delay; and (3) investigate the reason for disagreement. PATIENTS: 100 patients with ischaemic cardiomyopathy. SETTING: Tertiary referral cardiac unit. MAIN OUTCOME MEASURES: Dispersion in time interval from QRS onset to peak sustained systolic tissue velocity by TDI (SD-T(TV)) and to minimal systolic volume by RT3DE (SD-T(3D)) between 12 ventricular segments. RESULTS: RT3DE image quality was adequate for measurement of SD-T3D in 77 (77%) patients. In the whole population, SD-T(TV) was 40 (20) ms and SD-T3D was 8.3% (3.4%). RT3DE identified a smaller proportion of patients as having significant dyssynchrony than TDI (49 (64%) patients vs 32 (42%) patients; p<0.01). The correlation between SD-T(TV) and SD-T3D was poor (r = 0.11, p = NS). There was concordance between TDI and RT3DE in identifying the site of maximal mechanical delay in 12 (16%) patients. Validating the two techniques with anatomical M-mode (AMM) as a parameter of radial timing revealed better agreement with RT3DE than with TDI (chi2 = 11.8, p = 0.001). CONCLUSION: In patients with ischaemic cardiomyopathy, TDI and RT3DE show poor agreement for evaluating the magnitude of intraventricular dyssynchrony and the site of maximal mechanical delay. This may partly relate to their respective assessment of longitudinal versus radial timing.