Final answer:
c. Presence of U waves. U waves are an indication of hypokalemia in a client receiving IV furosemide for heart failure.
Step-by-step explanation:
When reviewing an ECG of a client receiving IV furosemide for heart failure, a nurse should identify the presence of U waves as an indication of hypokalemia. Hypokalemia refers to a low level of potassium in the blood, which can affect the electrical conduction system of the heart. U waves, which are small deflections following the T wave, are often seen in hypokalemia.