```json
{
    "no": ["no"],
    "yes": ["yes"]
}
```
Based on the given feature description and task, it seems that the feature "TRENT_S_n" represents the use of Trental in the ICU. The target variable is whether the patient shows chronic heart failure.

Since the feature is a categorical variable with two categories, "yes" and "no", we can conclude that the possible values of the feature for the target class "no" would be ["no"], indicating that there is no use of Trental in the ICU for patients without chronic heart failure.

Similarly, for the target class "yes" (indicating the presence of chronic heart failure), the possible values of the feature would be ["yes"], indicating the use of Trental in the ICU for patients with chronic heart failure.

Please note that this analysis assumes a direct relationship between the feature and the presence of chronic heart failure, and does not take into account any other variables or factors that might influence the outcome.