Left ventricular contraction was studied in 20 patients with mitral valve prolapse presenting with chest pain and/or palpitations. In this group of symptomatic patients systolic abnormalities were observed in 11 patients (55 p. 100): segmental hypokinesis was observed in 5 patients, hyperkinetic motion in 3 patients and an association of hyperkinetic and hypokinetic pareital motion was observed in the other 3 cases. Abnormalities of ventricular relaxation were found in 80 p. 100 patients. In all, 90 p. 100 patients in this selected group demonstrated systolic and/or diastolic abnormalities of the left ventricular myocardium. Symptoms (anginal chest pain, palpitations, neurotic symptoms) appear to be more frequent and more troublesome in patients systolic abnormalities. Hyperkinetic movement may be related to increased levels of circulating catecholamines. Segmental hypokinesis may be the result of focal ischaemia secondary to an abnormality of the coronary microcirculation. Both these abnormalities may be dependant on dysfunction of the autonomic nervous system. Further study is necessary to define the role of the autonomic nervous system in the myocardial abnormalities observed in this valvular syndrome.