This study investigates the autonomic cardiac function in pediatric patients with long COVID compared to healthy controls. Fifty-six pediatric patients with long COVID (mean age 10.3 ± 3.8 years) and 27 age-, sex-, and body surface area-matched healthy controls (mean age 10.4 ± 4.5 years) underwent standard 12-lead electrocardiography (ECG) and 24-h ECG Holter monitoring. Heart rate variability (HRV) parameters were assessed in both time and frequency domains, and echocardiographic studies were performed. Key findings include: - Pediatric patients with long COVID showed significant changes in HRV variables compared to healthy controls, with lower r-MSDD (root mean square of successive RR interval differences) and higher VLF, LF, and HF values. - No significant differences were observed in systolic and diastolic parameters by echocardiography. The study suggests that pediatric patients with long COVID have an imbalance of cardiac autonomic function, characterized by a relative predominance of parasympathetic tone, similar to findings in adult patients with long COVID. Further research is needed to clarify the clinical significance of this autonomic dysfunction and to explore potential therapeutic and preventive strategies.This study investigates the autonomic cardiac function in pediatric patients with long COVID compared to healthy controls. Fifty-six pediatric patients with long COVID (mean age 10.3 ± 3.8 years) and 27 age-, sex-, and body surface area-matched healthy controls (mean age 10.4 ± 4.5 years) underwent standard 12-lead electrocardiography (ECG) and 24-h ECG Holter monitoring. Heart rate variability (HRV) parameters were assessed in both time and frequency domains, and echocardiographic studies were performed. Key findings include: - Pediatric patients with long COVID showed significant changes in HRV variables compared to healthy controls, with lower r-MSDD (root mean square of successive RR interval differences) and higher VLF, LF, and HF values. - No significant differences were observed in systolic and diastolic parameters by echocardiography. The study suggests that pediatric patients with long COVID have an imbalance of cardiac autonomic function, characterized by a relative predominance of parasympathetic tone, similar to findings in adult patients with long COVID. Further research is needed to clarify the clinical significance of this autonomic dysfunction and to explore potential therapeutic and preventive strategies.