This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Unknown
Most common cardiac adverse effect of lithium is? 
Select and explain. 
A. Arrythmia, B. Cardiomyopathy, C. Bradycardia, D. Hypotension
C: Bradycardia
Answer: C: Bradycardia 
Explanation: 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.