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

Based on the given feature "B_BLOK_S_n" and the task of determining whether the patient has chronic heart failure, we can infer that the presence or absence of beta-blockers usage in the ICU does not provide enough information to directly determine chronic heart failure. 

The feature "B_BLOK_S_n" has two categories: "no" and "yes". However, without additional context or information about other features or variables, it is not possible to definitively answer the task based solely on this feature. Therefore, the lists for each target class contain only the available values within the feature.