Sunder, a young male was diagnosed as suffering from acute myeloid leukemia. He was started on induction chemotherapy with a doxorubicin-based regimen. Induction regimen was successful. Two months later, he presents to OPD with swelling of both the feet and breathlessness on climbing the stairs. He also complains he had to wake up many times because of breathlessness. Which of the following is most likely responsible for this patient's symptoms?