Abstract: Objective To study the effect of positive acceleration(+Gz) on myocardial microstructure of miniature swine with coronary stenosis. Methods A left anterior descending coronary stenosis model of Bama miniature swine was established. The flight environment was simulated. The maximum +Gz tolerance was measured. The microstructure of left ventricular anterior wall tissue sample taken from the swine was observed under light microscope and electron microscope, respectively. Results Light microscopy showed that the endocardium was well linked to myocardium and the myocardial cells were tightly arranged with no interstitial edema in sham operation group, the myocardial cells were partly deformed with slightly enlarged space and mild interstitial edema in mild stenosis group, the endocardial cells were edematous and the myocardial cells were irregularly arranged and ruptured with widely enlarged space in moderate stenosis group, the myocardial cells were significantly deformed and disarranged with significantly enlarged space and even deformed or exfoliated nuclei in severe stenosis group. Electron microscopy showed that the myocardial fibers and mitochondria were regularly arranged in sham operation group, the myocardial fibers were slightly blurred with accumulation of mitochondria and unclear inner ridge in mild stenosis group, the myocardial fibers were blurred with accumulation of mitochondria and vacuolation in moderate stenosis group, the myocardial fibers were ruptured and the mitochondria were severely deformed with concentrated cristae and some broken mitochondria in severe stenosis group. Conclusion The ventricular microstructure does not change significantly in miniature swine with mild coronary stenosis but changes significantly in those with moderate and severe stenosis at the maximum +Gz tolerance.