Objective To evaluate the transmural myocardial strain in three specific layers of the left ventricle at the papillary muscle level in short-axis view in SD rats before and after doxorubicin administration usmg myocardial layer-specific strain imaging based on two-dimensional ultrasound speckle tracking imaging (2D-STI),and to demonstrate the myocardial mechanical characteristics of doxorubicininduced early-stage acute cardiac toxicity in rats.Methods Thirty-two SD male rats weighing 300-350 g were randomly divided into a doxorubicin group (DOX group,n=16) and a control group (n=16).In the doxorubicin group,doxorubicin hydrochloride (concentration,2 mg/ml) was injected intraperitoneally at a single dose of 12 mg/kg,while the control group was given equal volume of 0.9％ sodium chloride solution.LVEDD,LVESD,IVSd,LVPWd,FS,and LVEF were measured and derived using two-dimensional gray-scale echocardiography at the left ventricular papillary muscle level in short-axis view at three time points (before administration and 24 and 48 hours after administration).The circumferential strain in the subendocardium,medium,and subepicardium at the left ventricular papillary muscle level in short-axis view were obtained using ultrasonic 2D-STI.The values of FS,LVEF,and the global myocardial circumferential strain in different layers of the left ventricular wall at the papillary muscle level in short axis view at three time points were compared between the two groups.After echocardiographic examinations at 48 h and 72 h,the hearts of three rats in each group were randomly selected,sliced,and HE-stained for myocardial pathological observation.Results In both groups,there was a circumferential strain gradient of the left ventricular wall at the papillary muscle level in the short-axis view:subendocardium ＞ medium ＞ epicardial myocardium.In the DOX group,the circumferential strain in the subendocardial myocardium decreased at 48 hours after DOX administration;the difference was statistically significant between the two groups (-25.13± 10.6 vs -17.04± 2.89,t=2.3,P ＜ 0.05).There was no significant difference in myocardial circumference strain in the three layers,as well as LVEDD,LVESD,IVS,LVPW,FS,or LVEF at three time points between the control group and DOX group (P ＞ 0.05).The pathological changes were mainly myocardial cell edema,vascular degeneration,myocardial nucleus atrophy,dissolution,interstitial edema,and capillary dilatation in the doxorubicin group,which were especially obvious in subendocardial cardiomyocytes.Conclusion 2D-STI technology based layer-specific strain imaging could be used to detect and quantitatively evaluate the deformation damage of the transmural left ventricular wall in SD rats.