A 69-year-old man is a new patient to your practice. He states that he has a heart condition but has never had a heart attack. He periodically experiences swelling of the lower legs and is taking a medication called digoxin (Lanoxin). He is also taking a "water pill." His vital signs are normal, but you notice some edema around his ankles.The MOST likely name for this patient's "heart condition" is:_______