Unusual increases in serum lactate dehydrogenase isoenzyme-5 activity caused by severe congestive cardiac failure: two case reports.

Two cases of congestive cardiac failure had unusually high activities of serum lactate dehydrogenase and lactate dehydrogenase isoenzyme-5. Values for isoenzyme-5 exceeding 87% of the total serum activity, and increases of 228- to 380-fold of the upper reference limit, are very uncommon.