The aim of our study was to evaluate myocardial functions with strain/strain rate echocardiography in asymptomatic patients having congenital aortic stenosis (CAS) with normal cardiac functions as determined by conventional echocardiographic techniques and comparing them with those of healthy controls. A total of 58 patients with various degrees of isolated CAS and 52 healthy controls were enrolled in this study. Conventional and two-dimensional speckle tracking (2DSTE) echocardiography were performed. Global longitudinal strain (LS) (−23.1 ± 3.6 and −23.8 ± 4.7), and longitudinal strain rate (LSR) (−1.49 ± 0.32 and −1.76 ± 0.39) values were lower, whereas circumferential strain (CS) (−25.9 ± 4.7 and −22.8 ± 6.4) and circumferential strain rate (CSR) (−1.82 ± 0.46 and −1.69 ± 0.49) values were greater in the patient group than in the control subjects. The difference was significant for global LSR and CS (p < 0.05) values. Regional analysis showed lower LS values in the basal part of the left-ventricular (LV) free wall and lower LSR values in the basal parts of both of the septum and free wall in the patient group (p < 0.05). CS values in the anteroseptal, posterior, and inferior walls were significantly greater in the patients (p < 0.05). 2DSTE detects subtle alterations in myocardial function in asymptomatic children with CAS. Impairment of LV long-axis function occurred earlier and was more prominent in basal parts of the interventricular septum and the free wall of the left ventricle.