Viral Myocarditis or Pericarditis: This is a common cause of irregular heartbeat in children, often resulting from a viral infection that affects the heart muscle or the sac surrounding the heart.

Supraventricular Tachycardia (SVT): A condition where the heart beats too quickly due to abnormal electrical impulses in the upper chambers of the heart. It's a common arrhythmia in children.
Ventricular Premature Beats: Early electrical impulses originating in the ventricles, causing the heart to beat prematurely. These are common in children and often benign.
Atrial Septal Defect (ASD) or Ventricular Septal Defect (VSD): Congenital heart defects that can lead to irregular heartbeats due to the abnormal flow of blood between the heart's chambers.

Hypertrophic Cardiomyopathy: A condition where the heart muscle becomes thickened, which can lead to arrhythmias and sudden cardiac death. Although less common, it's crucial to diagnose due to its potential severity.
Long QT Syndrome: A disorder of the heart's electrical activity that can cause sudden, uncontrollable, dangerous arrhythmias. It's essential to identify due to its risk of leading to sudden cardiac death.
Cardiac Tumors (e.g., Rhabdomyoma): Although rare, cardiac tumors can cause arrhythmias and have significant implications for the child's health.

Kawasaki Disease: An illness that affects the blood vessels and can lead to heart problems, including arrhythmias. It's more commonly associated with fever, rash, and other systemic symptoms.
Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC): A rare heart condition where the muscle in the right ventricle is replaced by fat and scar tissue, potentially leading to arrhythmias.
Congenital Heart Block: A rare condition where there's a blockage of the electrical impulses between the heart's upper and lower chambers, often associated with maternal autoimmune diseases like lupus.