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

Based on the feature "ritm_ecg_p_08" which describes the ECG rhythm at the time of admission to the hospital, the possible values are "no" and "yes". 

Since the task is to determine if the patient shows chronic heart failure, it is not necessary to include other values in the dictionary. The value "no" represents a sinus rhythm with a heart rate below 60, while the value "yes" indicates that the patient does have chronic heart failure.