Based on my prior knowledge, the presence of a first-degree AV block on an ECG (n_p_ecg_p_03 feature) can be indicative of chronic heart failure. To analyze the relationship between this feature and the presence of chronic heart failure, we can examine the distribution of n_p_ecg_p_03 values for each target class.

Here is the requested dictionary:

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

Explanation: 
- For the target class "no" (patients without chronic heart failure), the possible value of n_p_ecg_p_03 is "no".
- For the target class "yes" (patients with chronic heart failure), the possible value of n_p_ecg_p_03 is "yes".

Since the feature description only lists two possible categories, "no" and "yes", there are no other values to consider. Therefore, the dictionary only includes these two categories.