A 44-year-old female was had been diagnosed with endometrial stromal sarcoma metastatic to the lungs and underwent a radical hysterectomy. However, the patient's disease progressed with fever, dyspnea, orthopnea and fatige. A doppler echocardiogram was then performed and presented the alterations shown in Picture 1. After six cycles of adjuvant chemotherapy with doxorubicin and dacarbazine, there was complete resolution of the echocardiographic abnormal findings.

Question:
Based on the clinical history and imaging study, the most likely diagnosis is: