What could cause one lung to fill with blood? 82 yr old female. Congestive Heart Failure, severe heart blockage. Diabetes. Hemoglobin low.

Many causes. CHF, pulmonary hypertension, pulmonary embolism, arteriovenous malformation, cancer, pneumonia, anticoagulation just to name a few. This type of question is very difficult to answer because it involves a lot more questions from the doctor's point of view. Also, knowing whether blood was in the airways of the lung itself or around the lung in the chest cavity might help.