Review Question - QID 214452

A 50-year-old woman presents for preoperative evaluation for an open inguinal hernia repair. During the interview, the patient reports that she has been having more difficulty breathing and feeling more fatigued when gardening or walking with her husband. The patient's temperature is 97.8°F (36.6°C), blood pressure is 150/70 mmHg, pulse is 85/min, and respirations are 20/min. Physical exam is notable for a regularly irregular rhythm with radial artery palpation, clear audible breath sounds in all lung zones bilaterally, and mild pitting edema at her ankles bilaterally. Cardiac auscultation is notable for an S3 and a soft early systolic murmur at the apex. Of note, the patient had estrogen and progesterone receptor-negative, Her2-positive invasive ductal carcinoma of bilateral breasts, for which she achieved successful remission after treatment with trastuzumab and cyclophosphamide. Her most recent imaging 2 weeks ago confirming absence of the cancer and any potential metastasis marked the end of her chemotherapy. The patient has no additional medical history. What is the most likely etiology of this presentation?