Genetic analysis plays an important role in diagnostics of cardiovascular diseases. One of the diseases is long QT syndrome that results in an increased risk of ventricular tachycardia and sudden cardiac death. The syndrome may be caused by mutations in genes responsible for cardiomyocyte ionic channel functioning. The aim of this study is to examine genetics of long QT syndrome. Genetic analysis of 16 patients with long QT syndrome or suspicion of the syndrome was carried out. Long QT syndrome causing mutations, p.Ala178Pro, p.Val254Met, p.Gly325Arg in KCNQ1 and p.Thr613Met in KCNH2, and a long QT syndrome-associated polymorphism, p.Asp85Asn in KCNE1, were found in five patients. Family analysis of p.Ala178Pro and p.Val254Met mutations in KCNQ1 revealed the mutations carriers that had not demonstrated any syndrome manifestations before. In addition, a mutation, p.Gly604Ala in KCNH2, was found. The mutation has not been previously described and its role in long QT syndrome needs to be clarified.