After analyzing the relationship between the feature `n_p_ecg_p_06` and the task of determining if the patient shows chronic heart failure, the following dictionary can be created:

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

This dictionary indicates that for the target class "no" (no chronic heart failure), the value of `n_p_ecg_p_06` is always "no". And for the target class "yes" (chronic heart failure), the value of `n_p_ecg_p_06` is always "yes".

Since this feature is a categorical variable with only two possible values, there is no need to specify any possible values that are hard to predict, as both target classes have at least one corresponding value for `n_p_ecg_p_06`.