The aim of the investigation. To study the association between the degree, i.e., type of left ventricular hypertrophy and the prevalence of supraventricular and ventricular arrhythmias in hypertensive patients with left ventricular hypertrophy. Subjects and Methods. The investigation included a total of 192 patients (87 men and 105 women) aged between 43 and 90 years. The subjects were divided into three main groups with regard to the left ventricular hypertrophy type (concentric, eccentric and asymmetric hypertrophy) and three subgroups in relation to the degree of hypertrophy (mild, moderate and severe). Clinical and laboratory assessment also included cardiovascular risk factors, body mass index, body surface, chest x-ray and funduscopy. After a 48-hours medication discontinuance blood pressure and heart rate were measured, electrocardiography and echocardiography performed and ventricular and supraventricular arrhythmia frequency assessed by Holter monitoring and bicycle ergometry. Finally, patients with isolated systolic hypertension were separately evaluated. Results. The most frequent left ventricular hypertrophy is concentric (64%) followed by eccentric (27%). Severe left ventricular hypertrophy was found in 10% of patients. Patients with eccentric left ventricular hypertrophy had a significantly higher left ventricular mass index then those with concentric left ventricular hypertrophy (p=0.011). Supraventricular arrhythmias are more frequent than ventricular (93% vs. 80%, p=0.002). The prevalence of supraventricular premature beats was higher in the concentric and eccentric than in the asymmetric type (p=0.048) Their incidence correlates with the degree of left ventricular hypertrophy (significantly in men with the concentric type, (p=0.015). Atrial fibrillation, or paroxysmal supraventricular tachycardia were found in 43% of patients. The analysis showed no significant correlation between the prevalence of atrial fibrillation and/or paroxysmal supraventricular tachycardia and the degree (p=0.607) as well as the type of left ventricular hypertrophy (p=0.455). Complex ventricular arrhythmias during Holter monitoring were identified in over 40% of patients. There was no statistically significant difference between groups in frequency of simple (p=0.757) and complex (p=0.657, p=0.819, p=0.617, for polytopic, pairs and ventricular tachycardia, respectively) ventricular arrhythmias. Increased prevalence of ventricular arrhythmias was found for the moderate and severe degree in all types. In the concentric type the difference is statistically significant for simple ventricular arrhythmias (p=0.042). Ventricular tachycardia is more frequent in men than women (18% vs. 7%, p=0.024). The pulse pressure is significantly higher in the concentric type (p=0.00073) and slowly increases with the severity of hypertrophy (not significantly). QT and QTc intervals and QT dispersion are higher in more severe, concentric and eccentric types, not significantly (in men the length of QTc intervals increases with the degree of left ventricular hypertrophy, p=0.081). QT dispersion is significantly higher in men with severe left ventricular hypertrophy (p=0.047). The length of QTc intervals is significantly higher in the category of compelx ventricular arrhythmias (Lown III-V) then in the category of simple (p=0.037). For QTc the correlation has only tendency to increase. Conclusion. Concentric and eccentric types have a greater impact on the frequency of atrial arrhythmias, and moderate and severe concentric left ventricular hypertrophy represents the greatest risk for ventricular arrhythmias. The prevalence of cardiac arrhythmias (QTc interval and QT dispersion) correlates with the degree of left ventricular hypertrophy. The asymmetric type of hypertrophy does not represent a higher risk, nor does the isolated systolic hypertension. The pulse pressure appears to have the greatest influence on the geometry of the left ventricle. Patients with moderate and severe concentric and eccentric left ventricular hypertrophy should be always tested by Holter monitoring and bicycle ergometry and treated with maximally tolerable doses of antihypertensives, particularly with angiotensin converting enzyme inhibitors or angiotensin receptor blockers.