A cardiac replacement was a medical procedure which replaced the heart with a parthenogenic implant. The mortality rate for this procedure was less than 2.4%.
In 2365, Doctor Pulaski ordered Captain Picard to undergo a cardiac replacement at Starbase 515 in order to repair a prior faulty replacement. (TNG: "Samaritan Snare")
In 2374, Ishka suffered a possible heart attack or cardiac arrest and had to be given a new heart by Doctor Bashir. (DS9: "Profit and Lace")