Based on prior knowledge, I can analyze the relationship between the feature "nr_04" and the target variable "chronic heart failure". 

nr_04 represents whether the patient has persistent atrial fibrillation in their medical history. Atrial fibrillation is a known risk factor for chronic heart failure, as it can lead to structural changes in the heart and impaired cardiac function over time. Therefore, it is likely that patients with a history of persistent atrial fibrillation may show higher rates of chronic heart failure complications.

Based on this analysis, I will create a dictionary with the possible values of "nr_04" for each class of the target variable "chronic heart failure":

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

Please note that since the feature is categorical, we only have two possible values: "no" and "yes". The dictionary above simply maps these values to the respective target classes.