A 72-year-old man with a history of myocardial infarction presents with acute severe breathlessness. He is sitting upright, distressed, coughing pink frothy sputum. Observations: RR 30/min, SpO2 88% on air, BP 190/110 mmHg, pulse 120 bpm. Auscultation reveals bilateral basal crackles. After giving high-flow oxygen and sitting him upright, which intravenous medication should be given urgently?