INTRODUCTION: Cardiac mortality has increased in patients with epilepsy. Although majority of cardiac autonomic and ventricular function abnormalities were detected in ictal and postictal period, interictal epileptogenic activity may induce the autonomic imbalance as well. In our study, we aimed to investigate the interictal, subclinical cardiac changes in terms of cardiac autonomic balance via 24-hour Holter electrocardiography (ECG) and ventricular functions by tissue Doppler echocardiography (TDI) in children with newly diagnosed untreated idiopathic epilepsy. MATERIAL AND METHODS: Thirty children with newly diagnosed untreated idiopathic epilepsy (12 males, 18 females; mean age: 125.13鈥?/-鈥?5.2鈥痬onths) (patient group) and 40 healthy, age and body mass index (BMI)-matched children (18 males, 22 females; mean age: 129.43鈥?/-鈥?8.5鈥痬onths) (control group) were enrolled. Included patients underwent 24-hour Holter electrocardiographic and tissue Doppler echocardiographic study. RESULTS: Time domain measures were found significantly lower in the patient group. Mean high frequency (HF) values were significantly lower, and mean low frequency (LF) and mean LF/HF parameters were significantly higher in the patient group. Mean isovolumetric contraction time (ICT), isovolumetric relaxation time (IRT), and myocardial performance index (MPI) values were significantly higher, and mean ejection time (ET) values were significantly lower among the patients with untreated idiopathic epilepsy. CONCLUSION: We found that patients with untreated newly diagnosed epilepsy have a significant subclinical deterioration of left ventricular functions, and they also showed changes in heart rate variability (HRV) regarding the sympathovagal imbalance in interictal period. These findings can be related with increased cardiac mortality.