You are seeing a 70-year-old female in A&E who has presented with acute shortness of breath. She has a past medical history of heart failure. You decide to send her for a chest X ray as she has reduced air entry and dullness on percussion bilaterally in the lower lobes. The X ray shows blunting of costophrenic angles bilaterally. What is the most appropriate drug to relieve this patient’s symptoms as per the NICE guidelines?