Review Question - QID 212615

A 71-year-old man presents to his cardiologist with a 1-month history of increasing shortness of breath. He says that he is finding it very difficult to walk up the flight of stairs to his bedroom and he is no longer able to sleep flat on his bed because he wakes up choking for breath. His past medical history is significant for a myocardial infarction 3 years ago. On physical exam, he is found to have diffuse, moist crackles bilaterally on pulmonary auscultation and pitting edema in his lower extremities. Serum tests reveal an increased abundance of a product produced by cardiac myocytes. Which of the following most likely describes the function of this product?