"Pseudo-giant P-waves" and pericardial friction rub following chlorpromazine therapy

A patient is presented who manifested two previously undescribed complications of chlorpromazine therapy: a transient pericardial friction rub and "pseudo-giant P waves". After slowing of the heart rate, the "giant P-waves" proved to be superimposed U and P-waves. His history demonstrates the protean and at times unusual complications of chlorpromazine therapy and illustrates the dramatic therapeutic effects diphenhydramine may have in reversing some of this toxicity.