```json
{
    "no": ["M", "F"],
    "yes": ["M", "F"]
}
```
Based on prior knowledge, there is no specific relationship between the patient's sex and the presence of heart disease. Both male and female patients can have heart disease, and both male and female patients can have no heart disease. Therefore, the possible values for the feature "Sex" are the same for both the "yes" and "no" target classes, which are "M" (male) and "F" (female).