```json
{
    "no": ["no"],
    "yes": ["yes"]
}
```
Based on the given task, the target variable is whether the patient shows chronic heart failure. The feature "zab_leg_04" represents whether the patient has chronic pneumonia in the anamnesis. 

Since "zab_leg_04" is a categorical variable with categories "no" and "yes", we can directly map the feature values to the target classes. If "zab_leg_04" is "no", then the patient does not have chronic pneumonia in the anamnesis and does not show chronic heart failure. If "zab_leg_04" is "yes", then the patient has chronic pneumonia in the anamnesis and may show chronic heart failure.

Therefore, the possible values of "zab_leg_04" for the target class "no" are ["no"] and for the target class "yes" are ["yes"].