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

Based on the feature description, the possible values for the feature "np_04" are 'no' and 'yes'. Since the task is to determine whether the patient shows chronic heart failure or not, we can assume that if the patient has a history of third-degree AV block (np_04 = 'yes') in the anamnesis, it is likely related to chronic heart failure. On the other hand, if the patient does not have a history of third-degree AV block (np_04 = 'no'), it suggests that chronic heart failure is not present. Therefore, the possible values of the feature "np_04" for the target class 'no' are ['no'] and for the target class 'yes' are ['yes'].