Which nursing action is most important after receiving a client's complaints of left jaw pain and nausea?

The most important nursing action after a client reports left jaw pain and nausea is to perform a prompt cardiac assessment. These symptoms can be indicative of a cardiac issue, such as angina or myocardial infarction, especially considering that left jaw pain is a classic sign associated with heart problems.

A cardiac assessment typically includes checking vital signs, obtaining an ECG, and monitoring the client's level of consciousness. This action is critical because timely recognition of potential cardiac events can be life-saving and can influence treatment decisions. Being vigilant for cardiac complications allows for immediate intervention, which is vital in cases where the client may be experiencing a heart attack, where every minute counts.

Offering comfort measures, administering antiemetics, or notifying the physician are important nursing actions as well but are secondary to the need to assess the client's cardiac status, which may help identify a more serious condition that requires immediate intervention. Thus, the priority is ensuring the client’s safety and addressing any potential life threats that may arise from presenting symptoms.