A 45-year-old woman underwent a modified radical mastectomy 4 years ago. She was treated for multiple bone metastases with cyclophosphamide, doxorubicin, and fluorouracil for 6 months. She is complaining of exeion on exercise, swelling of the legs, and swelling around eyes in the morning. On examination, she has bilateral rales in the lungs. S1, S2 audible, S3 and S4 gallop is present. Her BP is 149/117 mm Hg, PR is 80/min, and RR is 18/min. What is the MOST likely cause of her cardiac condition?