Final answer:
The nurse should first administer nitroglycerin as prescribed.
Step-by-step explanation:
After hearing a sound during a cardiac assessment, the nurse should first administer nitroglycerin as prescribed. If the client recently had a myocardial infarction, the sound could be due to angina or a heart attack. Nitroglycerin helps to relax the blood vessels and improve blood flow to the heart, reducing the symptoms of angina.
Assessing the client's blood pressure is important, but it may not be the immediate priority in this situation. Documenting the finding in the medical record can be done after taking appropriate action, and notifying the healthcare provider should be done if the client's condition worsens or if there are other concerning symptoms.