A 63-year-old man arrives at the ED in an ambulance, complaining of a persistent, dull epigastric pain radiating to the interscapular region; the pain began 2 days ago. The nurse notes that he is alert and has good coloring and that his skin is warm and dry. Vital signs include right-arm blood pressure (BP) 120/60 mmHg, left-arm BP 220/100 mmHg, right radial pulse 2+, and left radial pulse 3+. The nurse notes bilateral basilar crackles and a systolic cardiac murmur at the second right intercostal space. The patient has a 33-year history of hypertension, for which he is taking medications. The physician prescribes an antihypertensive agent for the patient. The main objective of therapy is to maintain: