The heart has an inbuilt electrical system that tells it when to pump and when to relax. This keeps the heart in order and ensures good effective contractions (pumping) rather than something disorganised. In some people the time taken for the heart to relax (repolarise) is longer than it should be. If the next electrical signal to pump catches up with the previous signal to relax the heart can become confused, lose control and enter a strange ineffective pumping rhythm. Fortunately this loss of co-ordination is uncommon, it is however serious. Late relaxation or repolarisation of the heart is known as Long QT (because the Q wave and T wave are the parts of of the ECG - heart trace - from which this relaxation is measured).