The aim of presented thesis was to evaluate the factors influencing on the electrical instability of the left ventricle. The analysis was done in 150 patients aged 63.4 ± 10.4 years, treated for hypertension, without any clinical symptoms of heart failure. In all patients the questionnaire, anthropometric and blood pressure measurements, echocardiography, standard ECG recordings with manual measurement of QT interval duration and its dispersion, as well as signal-averaged electrocardiogram with identification of ventricular late potentials were performed. A risk of arrhythmogenesis in patients with arteria! hypertension is characterized by composed mechanism, but the most important risk factor seem to be left ventricular hypertrophy and its deteriorated geometry, as well as diastolic dysfunction. Left vcentricular hypertrophy seem to present a structural basis of arrhythmia, its impaired geomertry might be responsible for inhomogenity of repolarization. Diastolic dysfunction also potentiates electrical instability; QT prolongation seems to be related to impairment of early phase, and worsening of SA-ECG parameters - later phases of diastole. Such factors as female sex or high BMI might also potentially pqtentiate risk of ventricular arrhythmia in hypertensive patients.