```json
{
    "no": ["no"],
    "yes": ["yes"]
}
```
Based on the feature description and task, it seems that having premature atrial contractions in the anamnesis (nr_01) is relevant to determining if the patient has chronic heart failure. The feature is presented as a categorical variable with two possible values: 'no' and 'yes'. In this case, it is reasonable to assume that if a patient has premature atrial contractions in their medical history, it might be an indication of chronic heart failure.

The dictionary provided above shows that for the target class "no" (patients without chronic heart failure), the possible value for the feature nr_01 is only "no". Similarly, for the target class "yes" (patients with chronic heart failure), the only possible value for the nr_01 feature is "yes".

This analysis suggests that if a patient has premature atrial contractions in their medical history (nr_01 = "yes"), it is likely that they have chronic heart failure. Conversely, patients without premature atrial contractions (nr_01 = "no") are unlikely to have chronic heart failure.