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

Based on the given feature and task, the feature `n_p_ecg_p_12` represents the presence or absence of Complete Right Bundle Branch Block (RBBB) on the Electrocardiogram (ECG) at the time of admission to the hospital. 

Since the task is to determine whether the patient shows chronic heart failure, and there is no information about the relationship between `n_p_ecg_p_12` and chronic heart failure, it is difficult to predict how this feature relates to the target.

Therefore, the possible values for each target class are:

- For the target class `no`: The feature value can only be "no".
- For the target class `yes`: The feature value can only be "yes".

However, since there is no additional information available to analyze the relationship between `n_p_ecg_p_12` and chronic heart failure, there are no other possible values for this feature in the target classes.