Most parents associate Lyme disease with a tick bite, a bull's-eye rash, and a course of antibiotics. That picture is broadly correct, but it is incomplete. In a small proportion of children, Lyme disease can affect the heart directly, disrupting its electrical conduction system, inflaming the heart muscle, and in some cases triggering longer-term autonomic nervous system dysfunction and causing symptoms related to that. Understanding when and why the heart should be checked is important  because cardiac involvement in Lyme disease is frequently missed as the initial symptoms can be very mild and can be easily missed.

‍

Heart Conduction Problems

The most common cardiac manifestation of Lyme disease in children is atrioventricular (AV) block, a disruption of the electrical signals travelling from the upper to the lower chambers of the heart. Inflammation caused by the Borrelia bacterium can damage the conduction pathway, slowing or completely blocking the electrical signal. First-degree AV block is the mildest form and is often asymptomatic. It is detected primarily on an ECG. Second-degree AV block causes intermittently dropped beats, producing at times dizziness or palpitations. The third-degree (complete) AV block is the most serious type: no electrical signals reach the ventricles as the electrical impulse is completely blocked between the atria and the ventricle. In this setting the heart relies on a slow backup rhythm that can cause fainting or rarely more significant problems. Published paediatric data report first-degree block in around 28% of affected children, with complete block in approximately 17%. The critical reassurance for parents is that AV block caused by Lyme disease is almost always temporary. With appropriate antibiotic treatment, conduction abnormalities resolve in the vast majority of cases, typically within one week for advanced block. Temporary pacing is occasionally needed during the acute phase, but permanent pacemaker implantation is virtually never required.

‍

Heart Muscle Inflammation

Lyme disease can also inflame the heart muscle itself. Lyme myocarditis is reported in roughly 27% of children with Lyme carditis. In most cases it is mild, with transient reduction in the heart function. Function usually recovers fully with treatment. Rarely, it can be fulminant, presenting with breathlessness, poor feeding in infants, or collapse, requiring urgent hospital admission. A small body of evidence suggests that in exceptional cases, persistent myocardial inflammation may lead to dilated cardiomyopathy as a late complication, which is why follow-up echocardiography after significant Lyme carditis is advisable.

‍

The Risk of Dysautonomia

One of the less recognised consequences of Lyme disease in children is post-infectious dysautonomia, particularly postural orthostatic tachycardia syndrome (POTS). The autonomic nervous system, which controls heart rate, blood pressure, temperature, and digestion, can be damaged by infection-related inflammation and immune dysregulation. A child with Lyme-related POTS experiences an excessive rise in heart rate on standing (40 beats per minute or more in adolescents), along with dizziness, fatigue, brain fog, palpitations, and difficulty tolerating prolonged standing. These symptoms are frequently misattributed to anxiety, school avoidance, or deconditioning. Research from several leading centres has established the association between Lyme disease and POTS, with ongoing studies investigating prevalence and treatment. Recognising this connection in children requires a high degree of clinical suspicion, particularly when symptoms persist after apparently successful antibiotic treatment. Clues might be living in the countryside or wooded areas, having pets living at home or a history of tick bytes.

‍

Clinical Presentation and When to Suspect Cardiac Involvement

Symptoms that should raise concern include new-onset dizziness, fainting, palpitations, chest tightness, unusual fatigue, or breathlessness on exertion in a child with confirmed or suspected Lyme disease. In younger children, irritability, poor feeding, or reduced activity may be the only signs. Importantly, half of children with ECG evidence of Lyme carditis in one large multicentre study had no cardiac symptoms at all. NICE guidelines recommend considering Lyme disease in any child presenting with unexplained heart block or pericarditis, and advise that the diagnosis should not be excluded simply because the child does not recall a tick bite.

‍

Testing

An ECG is the first and most important investigation, capable of detecting AV block and other conduction abnormalities immediately. An echocardiogram assesses heart muscle function and identifies pericardial effusion. Lyme serology (two-tier testing) confirms the infection, though early results can be falsely negative. Cardiac biomarkers (troponin and NT-proBNP) can help identify ongoing myocardial injury. ECG Holter monitoring for 24 hours or longer periods is usually able to capture intermittent conduction disturbances. For children with suspected post-Lyme dysautonomia, an active standing test or formal tilt table test can point to the diagnosis of POTS.