In approximately 10-20% of all sudden deaths, no structural cardiac 
abnormalities can be identified. Important potential causes of sudden cardiac 
deaths in the absence of heart disease are primary electrical diseases such as 
Brugada syndrome, long QT syndrome (LQTS), short QT syndrome (SQTS), and 
catecholaminergic polymorphic ventricular tachyarrhythmias (CPVT). The resting 
ECG and the ECG under exercise are pivotal for the diagnosis of ion channel 
diseases. Molecular genetic screening can reveal underlying mutations in a 
variable degree among the cardiac ion channel diseases in up to 70% (LQTS) and 
may identify individuals with incomplete penetration of the disease. In patients 
with primary electrical diseases, specific clinical triggers for arrhythmic 
events such as syncope or sudden cardiac death have been identified including 
exercise, strenuous activity, auditory stimuli, or increased vagal tone. Young, 
otherwise healthy individuals are likely to be involved in sports activity. 
Therefore, special attention has to be given to advise these patients. 
Competitive sports and vigorous exercise are contraindications in almost all 
patients. Even recreational exercise may have to be avoided in phenotypically 
overt patients or silent gene carriers depending on the underlying disease.