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

Based on the given feature description and task, the ritm_ecg_p_08 feature represents the ECG rhythm at the time of admission to the hospital. It has two categories: "no" and "yes". 

For the target class "no" (chronic heart failure not present), the possible value for ritm_ecg_p_08 is "no". 

For the target class "yes" (chronic heart failure present), the possible value for ritm_ecg_p_08 is "yes". 

Since there are no other values or categories mentioned for ritm_ecg_p_08, the dictionary only includes the possible values "no" and "yes" for the respective target class.