Stress and sudden death. The case of the long QT syndrome. The idiopathic long QT syndrome (LQTS) represents a unique clinical example of stress-related sudden cardiac death. LQTS is characterized by the association of several distinctive electrocardiographic features, among which prolongation of the QT interval is the best known, with life-threatening arrhythmias that usually occur under conditions of physical or psychological stress. Effective therapies exist and are represented by antiadrenergic interventions; beta-adrenergic-blocking agents are the treatment of choice. When they fail, left cardiac sympathetic denervation has also proven to be very effective. The latter result suggests a role for alpha-adrenergic mechanisms in the arrhythmias of LQTS. The stressors more frequently associated with syncopal events in LQTS patients include fear, exercise fraught with emotions, swimming, and awakening because of a loud noise. Experimentally, life threatening arrhythmias have been induced during a highly emotional situation in conscious cats with normal hearts in which right stellate ganglia have been ablated, resulting in QT interval prolongation. This selective denervation creates a sympathetic imbalance of the type proposed by one of the pathogenetic hypotheses for LQTS. 