QT interval prolongation occurs in athletes and causes concerns, as it may indicate the life-threatening long QT syndrome (LQTS). Clinical and genetic testing identify those clearly affected by LQTS but in many no disease-causing mutations are found and diagnosis remains uncertain while they are barred from competitive sports. The investigators hypothesize that several cases represent an acquired form of LQTS, akin to drug-induced LQTS, caused by exercise training acting as a trigger or second hit on a genetic predisposition. The investigators will use next generation sequencing to screen major and minor LQTS genes plus common and rare variants modulating the QT interval in athletes with a QTc\>450ms (cases) and in those with a QTc\<430ms (controls). Thus, the investigators will quantify the presence of LQTS in athletes and will also focus on those who normalize their QTc after detraining, as this points to activation of stretch-receptors. The investigators will clarify QT prolongation in athletes and contribute to correct diagnosis.