Purpose: The maximal elastance ( Emax) of myocardium has been established as a reliable load-independent contractility index. Recently, we developed a noninvasive method to measure the regional contractility using gated myocardial SPECT and arterial tonometry data. In this study, we measured regional Emax ( rEmax) in the patients who underwent coronary artery bypass graft surgery (CABG), and assessed its relationship with other variables. Materials and Methods: 21 patients (M:F=17:4, 58±12 y) who underwent CABG were enrolled. 201Tl rest/ dipyridamole stress 99mTc-sestamibi gated SPECT were performed before and 3 months after CABG. For 15 myocardial regions, regional time-elastance curve was obtained using the pressure data of tonometry and the volume data of gated SPECT. To investigate the coupling with myocardial function, preoperative regional Emax was compared with regional perfusion and systolic thickening. In addition, the correlation between Emax and viability was assessed in dysfunctional segments (thickening <20% before CABG). The viability was defined as improvement of postoperative systolic thickening more than 10%. Results: Regional Emax was slightly increased after CABG from 2.41±1.64 (pre) to 2.78±1.83 (post) mmHg/mL. Emax had weak correlation with perfusion and thickening (r=0.35, p<0.001). In the regions of preserved perfusion (≥60%), Emax was 2.65±1.67, while it was 1.30±1.24 in the segments of decreased perfusion. With regard to thickening, Emax was 3.01±1.92 mmHg/mL for normal regions (thickening ≥40%), 2.40±1.19 mmHg/mL for mildly dysfunctional regions (<40% and ≥20%), and 1.13±0.89 mmHg/mL for severely dysfunctional regions (<20%). Emax was improved after CABG in both the viable (from 1.27±1.07 to 1.79±1.48 mmHg/mL) and non-viable segments (from 0.97±0.59 to 1.22±0.71 mmHg/mL), but there was no correlation between Emax and thickening improvements (r=0.007). Conclusions: Preoperative regional Emax was relatively concordant with regional perfusion and systolic thickening on gated myocardial SPECT. In dysfunctional but viable segments, Emax was improved after CABG, but showed no correlation with thickening improvement. As a load-independent contractility index of dysfunctional myocardial segments, we suggest that the regional Emax could be an independent parameter in the assessment of myocardial function.(Korean J Nucl Med 39(4):224-230, 2005)