QT interval prolongation is associated with an increased risk of life-threatening ventricular arrhythmias (including polymorphic ventricular tachycardia, also called torsades de pointes) and sudden cardiac death. One of the most common causes of acquired QT interval prolongation is the effect of certain drugs. To date, almost all existing drug groups have representatives with QT-lengthening effect, the realization of which, especially when combined with the so-called risk factors for QTC lengthening (modifiable - bradycardia, electrolyte abnormalities, drug interactions, overdose of QT-lengthening drugs and non-modifiable - female gender, older age, hereditary conditionality, the presence of structural heart disease, liver and/or kidney disease), leads to the development of clinically significant manifestations and complications associated with QTc prolongation, including fatal. Most pronounced QT-lengthening effect has representatives of anti-arrhythmics (IA, IC and class III), antipsychotics, antidepressants, antibiotics (macrolides and fluoroquinolones), antihistamines, anticancer and antifungal agents, prokinetics, lipid lowering drugs and diuretics, excluding potassium-sparing. Awareness and adequate assessment of the potential QTc prolongation ability of a drug administered to a patient, monitoring and correction of factors that determine and increase the risk of drug-related of the QTc prolongation, ECG monitoring, as well as the complete elimination of all drugs that potentially cause the QT interval prolongation, - the most important therapeutic and prophylactic measures to prevent or to stop the arrhythmogenic drugs effects.