A 78-year-old man with known heart failure with reduced ejection fraction presents with acute worsening breathlessness, orthopnoea and paroxysmal nocturnal dyspnoea. He has bilateral basal crackles, elevated jugular venous pressure and pitting ankle oedema. His current medications include Ramipril and Bisoprolol. Observations show BP 130/70 mmHg, oxygen saturation 93% on air. What is the most appropriate immediate pharmacological treatment in the emergency department?