Arrhythmias in the young are common and usually benign but may be life altering or lethal. Arrhythmias may begin at any age, from in utero up to the later teenage years, with a higher incidence in early infancy and mid-adolescence. Newer investigative modalities such as event recorders to capture infrequent episodes have enhanced our ability to detect and treat arrhythmias. Empirical therapy without detecting arrhythmia does not meet the current standard of practice. A 12-lead electrocardiogram (ECG) should always be obtained when an arrhythmia is being considered because rhythm alterations may be quite subtle and not always identified on a rhythm strip. In addition, a thorough family history is required, with particular emphasis on sudden and premature death, syncope, and recurrent arrhythmias.

Depending on the age of the patient and the rate and type of rhythm disturbance, children with arrhythmias may have nonspecific signs and symptoms such as fatigue, malaise, poor feeding, nausea, and pallor, or they may have more typical symptoms of cardiac dysfunction such as palpitations (the disquieting awareness of the person's own heartbeat), lightheadedness, syncope, visceral chest pain, and dyspnea.

Premature beats are infrequently noted by young patients. Supraventricular tachyarrhythmias in infancy may be noted incidentally on a visit for other reasons, but, more commonly, infants with supraventricular tachycardia (SVT) have signs and symptoms of congestive heart failure: tachypnea, dyspnea, truncal diaphoresis, diminished pulses, pallor, hepatomegaly, and poor feeding, in addition to tachycardia. Older children and adolescents are able to verbalize discomfort, including palpitations, chest pain, dyspnea, and nausea, from various forms of SVT. Ventricular tachyarrhythmias frequently compromise cardiac output to a greater degree than SVT and have more overt signs of congestive failure, chest pain, syncope, dyspnea, and palpitations. Infants and children with moderate or greater bradycardia from advanced 2nd-degree and complete heart block also display signs and symptoms of inadequate cardiac output, including fatigue, reduced exercise capacity, pallor, presyncope, and syncope.