<prompt> Most common cardiac adverse effect of lithium is?ArrythmiaCardiomyopathyBradycardiaHypotension  <response>: Reference: Katzung, Basic Clinical Pharmacology, 13th ed., Pg. 748.The bradycardia-tachycardia sick sinus syndrome is a definite contraindication to the use of lithium because the ion further depresses the sinus node. T-wave flattening is often observed on the electrocardiogram but is of questionable significance. 