Which client should the nurse see first in the coronary care unit after myocardial infarction?

The client with third-degree heart block on the monitor should be seen first because this condition is a significant and immediate concern that can lead to serious complications, including deteriorating cardiac output and potential cardiac arrest. Third-degree heart block, also known as complete heart block, implies a complete failure of electrical conduction between the atria and ventricles. This can cause profound bradycardia and result in the heart being unable to effectively pump blood, putting the patient at risk for hemodynamic instability.

In contrast, while the other clients may also have concerning symptoms or situations, they do not present the same level of immediate danger. For example, the client experiencing dyspnea on exertion may indicate respiratory compromise, but it is less critical than stable versus unstable heart rhythms. The client with a prolonged PR interval might suggest a first-degree heart block, which is typically less urgent, and can often be monitored without immediate intervention. The client refusing medication is a pertinent issue for treatment compliance; however, it doesn't represent an acute life-threatening situation requiring immediate intervention like a third-degree heart block does.

Thus, prioritizing care for the client with third-degree heart block aligns with the urgent nature of cardiovascular emergencies and the need to stabilize the patient as quickly as possible.