The present study was designed to detect the arrhythmogenic effect of left ventricular hypertrophy, QTc prolongation and the relationship between the QTc duration and ventricular arrhythmias in patients with left ventricular hypertrophy secondary to essential hypertension. Sixty-eight hypertensive patients (51 male and 17 female, mean age 52+/-6 years) and 30 healthy normotensive subjects (22 male and eight female, mean age 49+/-6 years) were enrolled in the study. The frequency of ventricular arrhythmias was investigated with 24-h ambulatory electrocardiographic monitoring and grade 3 and 4 ventricular arrhythmias according to a modified Lown and Wolf classification were accepted as complex arrhythmias. The echocardiographic features of the patients were divided into five groups as follows: (1) normal left ventricular diameter and wall thickness, (2) concentric left ventricular hypertrophy, (3) asymmetric septal hypertrophy, (4) dilated left ventricle, (5) dilated and hypertrophic left ventricle. The frequency of complex ventricular ectopia and the QTc duration were estimated for each group and compared with Student's t-test. Left ventricular hypertrophy was detected in 38 of 68 patients (56%) with essential hypertension. In patients with left ventricular hypertrophy, the incidence of complex ventricular arrhythmias was two- and fivefold higher compared with patients without left ventricular hypertrophy and with controls, respectively. All of the patients with echocardiographic left ventricular dilatation had experienced complex ventricular arrhythmias. QTc duration correlated positively with left ventricular mass index and left ventricular internal diastolic dimension. The highest QTc intervals were detected in patients with left ventricular hypertrophy and complex arrhythmias. In patients with left ventricular hypertrophy, a QTc duration longer than 380 ms had a sensitivity of 74% and a specificity of 89% for detecting complex ventricular arrhythmias. It is concluded that patients with left ventricular hypertrophy have a higher incidence of complex ventricular arrhythmias and QTc prolongation in those patients can be a good marker for the increased risk of arrhythmias.