Left anterior hemiblock (LAHB) is a relatively common disturbance of ventricular conduction which can be an indicator of early conduction system disease. In an effort to better understand this condition, phase analysis of resting radionuclide ventriculograms (RVG) was used to evaluate five patients with LAHB and six normal patients with particular reference to the phase angle difference between the septum and the postero-lateral wall. All patients had normal ejection fractions and visually normal wall motion on RVG. Visual analysis of phase images showed significant differences between the LAHB and normal patients' LV contraction synergy (p < 0.03) with a delay in septal contraction versus the postero-lateral wall. Four of five patients with LAHB were outside 2 standard deviations of the normal range. Regional quantitative analysis of phase angle differences between posterolateral and septal walls tended to show this difference between normals and LAHB (p = 0.08) as well. Three of five patients with LAHB were outside 2 standard deviations from the normals' mean. There were no significant differences between the standard deviations, skewness, or kurtoses of phase angle histograms of LAHB versus normal patients. Phase analysis can identify some patients with LAHB by both visual and quantitative analysis. The ability to detect and possibly quantitate subtle conduction abnormalities such as LAHB may result in a better understanding of such conduction system diseases.