```json
{
	"no": ["no"],
	"yes": ["yes"]
}
```

Based on the given feature "B_BLOK_S_n" which represents the use of beta-blockers in the ICU, the possible values are "no" and "yes". Since the task is to determine if the patient shows chronic heart failure, the feature "B_BLOK_S_n" is indicative of whether or not the patient is using beta-blockers in the ICU. 

If the patient is not using beta-blockers ("no"), it does not provide any evidence of chronic heart failure. If the patient is using beta-blockers ("yes"), it also does not provide any evidence of chronic heart failure. 

Therefore, the values for the feature "B_BLOK_S_n" for both target classes ("no" and "yes") are "no" and "yes" respectively.