Cardiac arrhythmias are frequent manifestations of hereditary connective tissue disorders (HCTD). Such HCTD as Marfan syndrome (MS), the primary mitral valve prolapse are characterized by frequent supraventricular and ventricular extrasystoles, prolonged PQ and QT interval, reduced heart rate variability and frequent findings of other predictors of heart arrhythmias. Cardiac arrhythmias as well as their predictors in patients of young age with marfanoid habitus (MH) were not previously evaluated.
 Materials and methods. A total number of 238 patients of young age were examined. All patients received phenotypic and anthropometric screening and Holter ECG. Cardiac arrhythmias, duration of QT interval (QTc), QT dispersion (QTd), heart rate variability and heart rate turbulence were estimated.
 Results for young people with MH as compared with the control group are characterized by frequent detection of paired (42.6% vs 9.7%, p= 0.00001), group (17.0% vs 4.2%, p = 0.01) supraventricular extrasystoles, ventricular extrasystoles in pathological quantity (10.6% vs 1.4%, p = 0.02). Pathological value of heart rate turbulence is detected significantly more frequently in individuals with MH. During evaluation of variability a significant decrease in all spectral (HF, LF, VLF), as well as most statistical (SDNN, pNN50) indicators was revealed. Patients with MH are characterized by prolonged QT interval (QTc threshold in 480 ms overcomes 21% of boys with MH, p = 0.00001) and increase the variance of the QT interval (threshold of 50 ms overcomes 37.5% of girls with MH, p = 0.0004).