ABSTRACT Background: in patients with primary mitral valve prolapse (MVP), the predictors of the complex ventricular arrhythmias are not fully studied and the QT variability index (QTVI) is not tested before. Objectives: This study aimed to evaluate the relation between the QTVI and the complex ventricular arrhythmias in patients with mitral valve prolapse. Methods: 32 patients with MVP were grouped according to presence or absence of complex ventricular arrhythmias. The prolapse grade, the mitral regurgitation degree, leaflet thickness, QT, QTc as well as QTVI were assessed using echoDoppler, standard 12 lead ECG and 24 hours ECG Holter. Our results showed: significantly higher grade MVP (score 8, 9) was present in 40% versus 5.9%, greater leaflets thickness was present in 5.40.8 versus 4.50.8, higher MR degree sever MR was present in 33.3% versus 0%, higher QT dispersion was 4414 versus 2710, higher QTVI -0.700.30 versus -0.890.2 in patients with MVP and complex ventricular dysrrhythmia than those without. (P = 0.03, 0.005, 0.013, 0.001, 0.045) respectively, increased QTVI is a powerful independent predictor of complex ventricular dysrrhythmias. We recommend to consider all these significant parameters including increased QTVI during mitral valve prolapse risk stratification.