Objective Magnetic resonance imaging (MRI) and pathological analysis were performed on Isca1myocardial conditional knockout rats to explore whether Isca1 myocardial conditional knockout elicits abnormal cardiacstructures in newborn rats. Methods Bred Isca1 myocardial conditional knockout rats and the genotyping and knockoutefficiency of Isca1 were verified by PCR. MRI was performed on the postnatal 0. 5 d and 2. 5 d Isca1 myocardial conditionalknockout rats. Pathological examination using H&E staining and transmission electron microscopy were performed on themyocardial tissues of postnatal 2. 5 d Isca1 myocardial conditional knockout rats. Results The knockout efficiency of Isca1myocardial conditional knockout rats was more than 78%. Compared with wild type rats, the 0. 5 d Isca1 myocardialconditional knockout rats showed no significant dilatation; however, the right ventricles of 2. 5 d Isca1 myocardialconditional knockout rats showed a tendency to dilate. Moreover, the myocardial fibers of 2. 5 d Isca1 myocardial conditionalknockout rats were irregularly arranged and disordered losing hierarchy or polarity. Part of the myocardial fibers showeddissolution and rupture. In addition, the sarcomere and Z-line were blurred, the sarcolemma was damaged, withmitochondrial swelling and rupture of cristae. Conclusion Isca1 myocardial conditional knockout results in abnorma lcardiac structures in newborn rats.