```json
{
   "no": ["no"],
   "yes": ["yes"]
}
```
Based on the given feature, the possible values for `ritm_ecg_p_04` are "no" and "yes". In this case, the dictionary shows that for the target class "no" (indicating no chronic heart failure), the feature value can only be "no". Similarly, for the target class "yes" (indicating chronic heart failure), the feature value can only be "yes".