Children with heart diseases have reduced physical activity (PA) levels relative to their peers, which in turn increases cardiovascular risk. To the best of our knowledge, physical fitness and objectively measured PA levels have not been previously studied in children with pacemakers. We evaluated PA levels and physical fitness in pediatric pacemaker patients compared to their healthy peers. Twenty-eight pediatric patients with pacemakers (15 female, 13 male; mean age 13.43 +/- 3.68 years) and 24 healthy subjects (14 female, 10 male; mean age 13.08 +/- 3.67 years) were included. Physical fitness was assessed using the Munich Fitness Test (MFT). SenseWear Armband metabolic Holter device was used to record the PA for 7 consecutive days. MFT total and sub-parameter scores were significantly lower in the patient group (p < 0.05). Patients' total and active energy expenditure, PA level, total distance, number of steps, and vigorous PA were significantly lower than those of healthy children (p < 0.05). Sedentary activity and light, moderate, and very vigorous PA durations were similar in both groups (p > 0.05). Duration of mean moderate to vigorous PA was higher than 60 min/day recommended in PA guidelines in both patients and healthy subjects. These results provide initial data on PA and fitness in children with pacemakers and suggest that physical fitness and activity levels in children with pacemakers are lower than in healthy peers. Appropriate exercise programs may improve PA levels in pediatric pacemaker patients. Awareness of the importance of PA should be raised among the parents and families of these children.