Review Question - QID 212783

A 76-year-old man presents to the physician with a complaint of episodes of shortness of breath during his daily walk around his neighborhood. He says that he has noticed his legs have become increasingly heavy and have appeared swollen for the past few months. Upon questioning, he confirms that he has shortness of breath when lying flat at night and sleeps with 2 additional pillows. Physical exam is notable for jugular venous distention and peripheral edema. His past medical history is significant for a diagnosis of multiple myeloma 1 year ago. An EKG is obtained (Figure A) and an echocardiogram (Figure B). A tissue biopsy would most likely reveal which of the following histological findings?