Answer:
The heart cells had not received adequate oxygen supply.
Step-by-step explanation:
Lactic acid is the result of a fermentation process that is happening in Susan's heart muscle. Fermentation is a process that occurs only in anaerobic environments, that is, environments with absence of oxygen. For this reason, we can conclude that the increased ratio of lactic acid to pyruvic acid in the heart of susan occurred due to the inadequate supply of oxygen to the heart cells.