```json
{
    "no": ["no"],
    "yes": ["yes"]
}
```
The feature "endocr_03" has only two possible values in the given categories, "no" and "yes". In this case, there is a clear relationship between the feature and the task. If the value of "endocr_03" for a patient is "no", it suggests that the patient does not have a history of thyrotoxicosis, and therefore it is less likely for them to show chronic heart failure. On the other hand, if the value is "yes", it indicates that the patient has a history of thyrotoxicosis, which might be associated with an increased risk of chronic heart failure.