Based on prior knowledge, it is likely that the presence of thyrotoxicosis in the medical history (endocr_03) could be related to chronic heart failure. 

To analyze the relationship between the feature endocr_03 and the task of determining if the patient shows chronic heart failure, we can examine the distribution of endocr_03 values for each target class.

Here is the analysis:

For target class "no":
- endocr_03 values: ['no', 'yes']

For target class "yes":
- endocr_03 values: ['no', 'yes', 'missing']

Based on this analysis, we can create the dictionary:

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

This dictionary represents the possible values of endocr_03 for each target class. It includes both the "no" and "yes" categories for both target classes. However, it does not include the "missing" category for the target class "yes" as it is hard to predict.