A well-documented association exists between the phenothiazines and the tricyclic antidepressants and such alarming side effects as cardiac arrhythmias, ECG changes, and even sudden death. Most disturbing is the fact that major and possibly fatal arrhythmias can occur in young adults without antecedent heart disease who are receiving therapeutic dosages of these psychotropic drugs (especially thioridazine). Further study of the cardiovascular side effects of psychotropic drugs is needed to clarify the association. In the meantime, it is mandatory that physicians individualize treatment programs that include these drugs and carefully monitor patient response.