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

Based on the given feature description, the n_r_ecg_p_03 feature represents the presence or absence of ventricular contractions on the electrocardiogram (ECG) at the time of admission to the hospital. Since the feature is categorical with two possible values 'no' and 'yes', we can directly map these values to the target classes 'no' and 'yes' respectively.

In the context of determining if the patient has chronic heart failure, the n_r_ecg_p_03 feature does not provide any additional information other than indicating the presence or absence of ventricular contractions at the time of admission. Thus, the presence or absence of ventricular contractions cannot be solely used to determine if the patient has chronic heart failure.