```json
{
    "no": ["no"],
    "yes": ["yes"]
}
```
Based on the feature description and the task, it seems that we need to determine whether the patient has chronic heart failure based on their use of beta-blockers in the ICU. 

Looking at the possible categories of the feature "B_BLOK_S_n", we can see that there are two possible values: "no" and "yes". 

To analyze the relationship between the feature and the task, we need more information about the target variable. If we have data on whether the patient has chronic heart failure or not, we can compare the distribution of the feature for each class to evaluate the relationship.

However, based on the given task and feature description alone, we can assume that if the value of "B_BLOK_S_n" is "no", it suggests that the patient does not use beta-blockers in the ICU and therefore might not have chronic heart failure. On the other hand, if the value is "yes", it suggests that the patient does use beta-blockers in the ICU, which might indicate a higher chance of having chronic heart failure.

Please note that without the actual data and additional information about the target variable, we cannot make a definitive analysis or provide more accurate predictions. The provided dictionary only represents the possible values of the feature "B_BLOK_S_n" within each class of the target variable.