The introduction of Gated SPECT cardiac imaging using technetium99 msesta MIBI offeredus the chance to study and document the phenomenon of stunning in the setting of acuteSTEMI. Aim of work was to study the impact of revascularisation using primary PCI on LVED and LVES volumesusing gated SPECT study. Our study included 27 pts presenting with acute STEMI eligible for primary PCI. All ptswere injected 25 mCi Tc99msesta MIBI on admission and acquisition of rest GSPECT MPIwas done after revascularization and within 6 hours of injection to get the first set ofimages assumed to get the initial functional parameters [before PCI]; LVEDV (EDV1),LVESV (ESV1) and LVEF (EF1). Another set of images was acquired 2-3 days later to get the second set of functional parameters [after PCI] (EDV2, ESV2, and EF2). A total of 27 pts (25 males) with acute STEMI were included, 5 pts were diabetic, 4hypertensive, 20 smoker, 6 dyslipidemic and 9 pts had +ve FH of CAD. Mean duration ofchest pain was (4.2 + 2.7 hours), mean door to balloon time was (1.5+1 hours).Seventeen pts had anterior STEMI and 10 had inferior. Upon coronary angiography theculprit vessel was LAD in anterior MI pts and RCA in inferior MI pts. Primary PCI wasconsidered angiographically successful (TIMI 2-3) in 26 pts and 13 pts had other vesselsinvolved (LAD in 5 pts, RCA in 5 pts, LCx in 4 pts and diagonal in 2 pts). There wassignificant reduction in EDV and ESV after PCI [ (129.4+36.3 vs.105+37 ml, p<0.0001) and(61.8+21.6 vs. 49.3+21 ml, p<0.0001) and significant increase in EF (53+9.8% vs.57.6+10%, p<0.0001).The ESV1 was higher with LAD as a culprit vessel whencompared to RCA (70+24 vs. 46+14 ml, p=0.009) and was insignificantly higher inmultivessel pts (65+27 vs. 58+22ml, p=0.6). EDV1 was insignificantly higher in LAD pts(135+30 vs. 118+29 ml, p=0.2) and with multivessel involvement (133+40 vs. 125+33 ml,p=0.5). EF1 was significantly lower in LAD pts, (48+9vs 60+6%, p=0.001) andinsignificantly lower in multivessel involvement (50+10 vs. 52+10(p=0.6) and there was nosignificant correlation between ESV1, EDV1 or EF1 and initial TIMI flow (p>0.05).ESV2 was significantly higher in LAD pts (56+20 vs. 36+16 ml, p=0.01). EDV2 wasinsignificantly higher in LAD pts (109+36 vs. 97+40 ml, p=0.4). EF2 was significantlylower in LAD pts (54+9 vs. 63+7%, p=0.014). EDV2, ESV2 or EF2 were not significantly correlated to TIMI flow post PCI or [TIMI pre-TIMI post) (p>0.05).Conclusion:Gated SPECT study in the session of acute STEMI may be used to assess the LVfunctional improvement after primary PCI. LVESV and LVEF are affected mainly by LADacute occlusion and not by multivessel involvement or TIMI flow in the setting of acuteSTEMI.