The case reported concerns a symptomatic transitory sinus node abnormality in a 75 years old woman treated with Lithium Carbonate (750 mg/d) for a manic-depressive psychosis. This patient, admitted to the hospital for bradycardia and repeated episodes of syncope was shown to present sinus pauses greater than 3 seconds. Lithium therapy was discontinued. 72 hours later electrophysiologic studies, performed to evaluate sinus node function, were normal. It is therefore the author's opinion that in patients receiving Lithium therapy who present syncope, dizziness, or bradycardia a sinus node abnormality of iatrogenic origin must be considered. The importance of this diagnosis is in the rapid reversibility of the sinus node dysfunction with discontinuation of therapy.