Aim of this study was to verify the prevalence of cardiac arrhythmias in subjects with mitral valve prolapse (MVP) and redundant leaflets in comparison with subjects with MVP without leaflets redundance. So, 60 subjects (aged 13 to 39 years), were subdivided in 3 groups on the basis of mitral leaflets shape at 2D-echocardiography; a continuous ECG monitoring (24 hours) was also performed. Arrhythmias were more frequent and more severe in the Group III (subjects with MVP and redundant leaflets), in comparison with both Group II (subjects with MVP without leaflets redundance) and Group I (control subjects). In particular, analysing the mean values of the single arrhythmias in the 24 hours, ventricular ectopic beats (VEB), were more frequent in Group II (p less than 0.01) and Group III (p less than 0.05) in comparison with Group I; the couplets and the runs of ventricular tachycardia were more frequent in Group III than in the other groups (p less than 0.001). The number of the subjects with a Lown class greater than 3 was higher in Group III than in the other groups (p less than 0.01). In conclusion, this study confirms that MVP is a disease presenting a large variability arrhythmic risk, that seems to be real only for a subgroup of these subjects.