```json
{
    "no": ["Flat", "Down"],
    "yes": ["Up"]
}
```
From prior knowledge, we can analyze the relationship between the feature "ST_Slope" and the task of determining if the patient has heart disease.

Patients with a "Flat" or "Down" slope of the peak exercise ST segment are more likely to not have heart disease, as indicated by the "no" target class. On the other hand, patients with an "Up" slope of the peak exercise ST segment are more likely to have heart disease, as indicated by the "yes" target class.

Therefore, the dictionary shows that the feature "ST_Slope" has the values "Flat" and "Down" associated with the "no" target class, indicating no heart disease, and the value "Up" is associated with the "yes" target class, indicating heart disease.