Polycythemia causing high output cardiac failure

My spouse has polycythemia Vera, dx about 6 years ago. She did well on hydrea 500mg daily until about 3 months ago. Her platelets began to rise. Her oncologist increased the hydrea to 1000mg per day. Her platelets came down . She was stable till about 5 weeks ago when she began to develop shortness of breath, with mild exercise, and even at rest. Work up to this point, including nuclear stress, echo, pulmonary function , blood gases, O2 saturation, ekg, chest CT for PE, troponin level have all been normal. Her hematocrit is 37, serum iron is low. She has never smoked, and there is no cardiac history in her family. We are currently waiting to visit her oncologist. My question for the group is does anyone have any first hand knowledge of high output cardiac failure secondary to a myeloproliferative disease such as polycythemia Vera or multiple myeloma ? Thanks for comment’s.