Final answer:
The nurse should monitor the client with heart failure most closely for excessive fluid volume.
Step-by-step explanation:
The nurse should monitor the client with heart failure most closely for excessive fluid volume. Hypervolemia, or excessive fluid volume, can occur in patients with heart failure, among other conditions. It is caused by the retention of water and sodium, and restoring homeostasis in these patients depends on reversing the condition that triggered the hypervolemia.