Mitral valve prolapse (MVP) is characterized by arrhythmias, atypical anginal chest pain and left ventricular (LV) wall motion abnormalities. The role of autonomic nervous system (ANS) as the origin of these disturbances is still debated. The aim of the study was to determine the possible interference between left ventricle (LV) mechanics and ANS. 35 consecutive patients with MVP (24 female, 11 male) (mean age 30 +/- 9 years), matched with a homogeneous control group, were examined by means of 2D-Echo during resting conditions and during sympathetic activation induced by passive orthostatism (90 degrees Tilting). At rest, no significant difference was found between the two groups regarding heart rate (HR), LV volume (LVV), ejection fraction (EF). Tilting produced a significant increase in HR (p less than 0.1) and LVV reduction (p less than .01) in both groups; on the other hand, EF did not change significantly. At 2D-Echo, LV abnormal wall motion at rest in 10/35 (29%) MVP, increasing to 17/35 (49%) was found during Tilting. This abnormality consisted in LV wall reduced systolic thickening and motion, localized in the antero-apical region in 11 patients (54%) and in the posterior wall in 6 patients (36%). Thirteen MVP patients with LV abnormal contraction patterns were re-examined after two weeks of beta-adrenergic blockade (200 mg Metoprolol orally per day). In all of them, LV abnormalities disappeared while LVV and EF remained unchanged. These data stress the role of the ANS in inducing LV abnormalities in patients with MVP.