Myocardial enzyme balance was a condition that needed to be monitored during cardiac implant surgery. The Starbase 515 surgeon who began Captain Jean-Luc Picard's secondary implant called for a check on this enzyme balance during the procedure. (TNG: "Samaritan Snare")
"my-ah-CARD-ee-el EN-zime" was the pronunciation of this medical condition's name from the script pronunciation guide. [1]