Based on prior knowledge, we can analyze the relationship between the feature "IBS_POST" and the task of determining if the patient shows chronic heart failure. 

The feature "IBS_POST" represents the presence of coronary heart disease (CHD) in the recent weeks, days before admission to the hospital. The possible categories for the feature are:

- "there was no СHD"
- "exertional angina pectoris"
- "unstable angina pectoris"

To determine if the patient shows chronic heart failure, we need to examine if any of these categories of "IBS_POST" indicate the presence of chronic heart failure.

To construct the dictionary, we need to identify the possible values of the feature "IBS_POST" for each target class (yes or no). 

Let's assume that "yes" represents the presence of chronic heart failure and "no" represents the absence of chronic heart failure.

Possible values of feature IBS_POST for target class "no" (absence of chronic heart failure) can be any category that does not indicate the presence of CHD. Therefore, in this case, the possible values are:

- "there was no СHD"

Possible values of feature IBS_POST for target class "yes" (presence of chronic heart failure) can be those categories that imply the presence of CHD. In this case, the possible values are:

- "exertional angina pectoris"
- "unstable angina pectoris"

The dictionary representing the relationship between the feature "IBS_POST" and the presence of chronic heart failure is as follows:

```json
{
	"no": ["there was no СHD"],
	"yes": ["exertional angina pectoris", "unstable angina pectoris"]
}
```