Final answer:
The etiology of the heart failure would be termed idiopathic.
Step-by-step explanation:
A young, otherwise healthy patient is admitted to the hospital with a diagnosis of heart failure of unknown cause. The etiology of the heart failure would be termed idiopathic.
Idiopathic means that the cause of the heart failure is unknown. In this case, there is no specific known cause for the heart failure in the young, healthy patient. Other options like iatrogenic, nosocomial, or acute do not accurately describe the case.