Based on the feature description, we are analyzing the relationship between the feature "IBS_POST" and the occurrence of chronic heart failure as the target variable.

To conduct this analysis, we need to examine the distribution of "IBS_POST" values for the two target classes: yes (chronic heart failure) and no (no chronic heart failure).

Here is the dictionary representing the relationship between the feature and the target:

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

Based on the available information, patients with the value "there was no СHD" for "IBS_POST" do not indicate chronic heart failure (target: no). On the other hand, patients with the values "exertional angina pectoris" or "unstable angina pectoris" for "IBS_POST" are likely to have chronic heart failure (target: yes).

Please note that this analysis is based on the provided feature description. If there are additional factors or information available, the relationship between the feature and target might change.