ECG must always be interpreted in respect to the age of the child. Modern recorders of twelve lead ECG often give a summary of the findings. The reliability of the interpretation varies markedly depending on the reference values used. The interpretation may be misleading, especially when the rhythm is evaluated. The summary often includes a comment like 'possible hypertrophy'. This may be due to high voltage measured in the recording of a single lead. Thus, the physician must always evaluate the ECG as an entity. Because of large individual variation and changes occurring with age the reference intervals are rather wide. ECG in children is not a very sensitive and accurate method for evaluating, for example, ventricular hypertrophy.