IntroductionThyroid hormone (TH) improves left ventricular (LV) remodeling and function after myocardial infarction (MI); however, the cellular basis is unknown.MethodsMI was produced by ligation of the LAD in female SD rats. Rats were divided into the following groups: (1) Sham MI, (2) MI, and (3) MI+T4 treatment (T4 pellet 3.3mg, 60 days release, implanted subcutaneously immediately following MI). Each group was further divided into two subgroups (n=9 per subgroup) for myocytes isolation and whole heart tissues collection eight weeks after surgery.ResultsMI resulted in LV chamber dilatation and functional impairment, with LV myocyte lengthening. T4 treatment after MI improved LV function, increased LV weight by 37%, increased LV myocyte volume and cross‐sectional area (CSA) by 13%, and increased non‐infarcted tissue area by 41%, but did not change the infarct perimeter or LV dimension (Table 1). The increase in LV myocyte volume accounted for only 1/3 of the increase in non‐infarcted tissue area, indicating an increased number of surviving myocytes accounted for the remaining portion. Based on our previously published paper, T4 treatment might help to preserve myocytes in the border zone after MI via its anti‐apoptotic effect.ConclusionsThese results suggest T4 treatment after MI can improve LV myocyte remodeling and preserve myocytes in the border zone.