Cardiovascular morbidity and mortality are higher in psychiatric patients than in the general population. In schizophrenic patients without cardiovascular history, long QT interval is a major risk factor for torsades de pointe and for sudden death. QT interval prolongation is a severe and underestimated dose-dependent adverse reaction triggered by several psychotropic drugs and by clinical situations such as polymedication, methadone maintenance treatment, electrolytic disturbances, cardiovascular history and congenital long QT syndromes. Systematic measurement of QT interval is recommended when psychotropic medications known to prolong it are introduced, as well as in clinical situations at risk. Stereoselective R-methadone administration (chiral switching) contributes to reduce the risk of QT prolongation.