A nurse is caring for a client who develops third-degree heart block with a heart rate of 30/min. Which of the following actions should the nurse take?

A. Digoxin slows conduction through the AV node and can worsen heart block. It is contraindicated in clients with third-degree (complete) heart block. B. The Valsalva maneuver can increase vagal tone and further slow the heart rate, making it inappropriate and potentially dangerous in complete heart block. C. Preparing the client for temporary pacing is the correct and immediate intervention for symptomatic third-degree heart block with a very slow heart rate (30/min), as this condition results in ineffective atrial-to-ventricular conduction and may lead to severe bradycardia and hemodynamic instability. D. Carotid sinus massage slows the heart rate and is used to treat supraventricular tachycardias, not bradyarrhythmias like third-degree heart block.