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

Based on the given feature "ANT_CA_S_n" and the task of determining if the patient has chronic heart failure, it appears that this feature directly provides information about the use of calcium channel blockers in the ICU. The possible values for this feature are "yes" and "no". 

Since the task is to determine if the patient has chronic heart failure, and the feature describes the use of calcium channel blockers in the ICU, it can be inferred that the feature may influence the likelihood of chronic heart failure. 

The dictionary indicates that for the target class "no" (indicating no chronic heart failure), the only possible value of the feature is "no". Similarly, for the target class "yes" (indicating chronic heart failure), the only possible value of the feature is "yes".

As there is only one value for each target class, it suggests that the presence of chronic heart failure is determined solely based on the value of the feature.