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

Based on the feature description and task, the feature "MP_TP_POST" represents whether the patient had paroxysms of atrial fibrillation at the time of admission to the intensive care unit or at a prehospital stage. For the task of determining if the patient shows chronic heart failure, the values of "MP_TP_POST" are categorized as either "no" or "yes".

In this case, the unique value for the target class "no" is "no", indicating that patients without paroxysms of atrial fibrillation do not show chronic heart failure. Similarly, the unique value for the target class "yes" is "yes", suggesting that patients with paroxysms of atrial fibrillation indicate the presence of chronic heart failure.

Please note that if there are any additional values for "MP_TP_POST" that are hard to predict or missing from the available data, they are not included in the dictionary. However, the dictionary ensures that the list for each target class is not empty.