[Prevalence of mitral valve prolapse in patients with premature ventricular contractions and the relationship between the prolapse and the types of premature contractions]. 
To assess the prevalence of mitral valve prolapse (MVP) in patients with premature ventricular contractions (PVCs), 109 patients with PVCs (M: 69, F: 40, 42 +/- 20 years; mean +/- SD) and 50 control subjects (M: 38, F: 12, 47 +/- 10 years) were studied by echocardiography.  MVP was diagnosed by two-dimensional echocardiography.  The criterion for mitral valve prolapse by two-dimensional echocardiography is extension of the mitral leaflet to the left atrial side beyond the plane of the mitral annulus.  In addition, 60 patients with PVCs were examined by 24-hour Holter ECG and scored by the Lown's classification.  Results were as follows: 1) MVP was detected more frequently in patients with PVCs than in the control subjects (22/109, 20% vs 3/50, 6%, p less than 0.05) by echocardiography.  2) PVC patients with MVP were significantly younger than patients without MVP (34 +/- 14 vs 47 +/- 21 yrs, p less than 0.05), but there were no significant differences between these two groups as to sex, left atrial diameter and left ventricular dimension.  3) The 24-hour Holter ECG revealed that the high grade PVCs (Lown grade III & IV) was more closely related to the absence of MVP (20/45, 44% vs 4/11, 36%), though this trend did not reach statistical significance.  It was suggested that MVP is not a major determinant of PVC, and life-threatening arrhythmias are more likely related to cases without MVP.