Impaired cardiac myocardial function may contribute to the risk for sudden unexpected death of a patient with epilepsy. This study aimed to investigate the effect of antiepilepsy drugs (AEDs) on cardiac function in pediatric epileptic patients using standard and tissue Doppler imaging (TDI) echocardiography. This hospital-based, prospective cross-sectional study investigated 52 epileptic children (mean age 9.3 ± 3.1 years) treated with AEDs (duration 2.4–10.0 years) and 36 healthy children (mean age 9.5 ± 4.0 years). In the epilepsy group, standard echocardiography showed increased left ventricular (LV) end-diastolic and end-systolic diameters, an increased LV mass index, and preserved ejection fraction. The patients also exhibited increased mitral peak A-wave velocity and mitral E-wave deceleration time as well as a decreased mitral E/A ratio. The E/Em ratio was significantly higher in the epilepsy group (5.6 ± 1.2) than in the control group (5.2 ± 1.1) (p = 0.016). In the epilepsy group, TDI showed an increased isovolumetric relaxation time and myocardial performance index (MPI). It also exhibited decreased early diastolic velocity (Em) and a decreased mitral annular displacement index in these patients. There were positive correlations between the LV lateral wall MPI (r = 0.231), septal MPI (r = 0.223), and LV mass index (p < 0.05) but no correlation with the duration of AED treatment. The authors detected subclinical ventricular dysfunction associated with AEDs at a preclinical stage. They suggest that TDI can be useful for determining the short- and long-term cardiac effects of AEDs.