Final answer:
A persistent cough is a common side effect of the ACE inhibitor captopril (Capoten) and would be a concern to report to the physician, as it can indicate the need for a change in treatment.
Step-by-step explanation:
The treatment of heart failure with captopril (Capoten) can have several adverse effects, but among those listed, the development of a persistent cough is a known side effect of ACE inhibitors such as captopril and would be cause for the nurse to report to the physician. This cough is due to the buildup of bradykinin in the respiratory tract. While diarrhea, dehydration, and facial flushing might occur with various medications and health conditions, the cough specifically is a common and well-documented side effect of captopril that could lead to patient discomfort and a potential change in medication strategy.