The authors review the literature on arrhythmias and ST changes, the principal causes of sudden death in the mid systolic click-late systolic murmur (SC-SM) syndrome, having recorded the ECG during sudden death of a patient with this syndrome by Holter monitoring. This would also appear to be the first reported case of sudden death recorded by this technique. It showed that death was caused by ventricular fibrillation which was preceded by a clinical and electrical episode of Prinzmetal angina. Hypotheses explaining the abnormalities of ventricular repolarisation and rhythm in so-called "idiopathic" SC-SM syndrome are reviewed. Special attention is paid to studies suggesting the participation of coronary spasm and autonomic nervous system disturbances. In conclusion, the authors underline: - the value of ambulatory electrocardiography in patients with the SC-SM syndrome and especially in a defined high risk group; - the value of testing for coronary spasm when coronary angiography is envisaged; - the need for better management with antiarrhythmic therapy. The indications of betablockade are discussed as these drugs are thought to favourise coronary spasm.