Background. A count-based method using technetium-99m sestamibi electrocardiography-gated myocardial perfusion single photon emission computed tomography imaging has been developed to extract the left ventricular (LV) regional phase of contraction (onset of mechanical contraction [OMC]) throughout the cardiac cycle. This study was performed to develop OMC normal databases and dynamic OMC displays for assessment of cardiac mechanic dyssynchrony. Methods and Results. LV regional phases were extracted from 90 enrolled normal subjects (45 men and 45 women) by use of the Emory Cardiac Toolbox and then submitted to statistical analysis to generate the normal databases. The LV OMC wave was dynamically propagated over the perfusion polar map by blackening either sequential phase bins or all past phases. The developed OMC normal databases consisted of peak phase (134.5° ± 14.3° for men and 140.2° ± 14.9° for women), phase SD (14.2° ± 5.1° for men and 11.8° ± 5.2° for women), and phase histogram bandwidth (38.7° ± 11.8° for men and 30.6° ± 9.6° for women), skewness (4.19 ± 0.68 for men and 4.60 ± 0.72 for women), and kurtosis (19.72 ± 7.68 for men and 23.21 ± 8.16 for women). Both statistical analysis and dynamic OMC displays were incorporated into a user interface as a diagnostic tool. Conclusion. The OMC normal databases and dynamic OMC displays should help clinicians evaluate cardiac mechanic dyssynchrony. Prospective clinical trials are needed to validate whether this tool can be used to select patients with severe heart failure symptoms who might benefit from cardiac resynchronization therapy. Copyright © 2005 by the American Society of Nuclear Cardiology.