What does a cardiac cough sound like?

Heart failure: Assuming you are referring to the cough associated with heart failure (congestive heart failure), it is a persistent moist cough which is not relieved until the heart failure is adequately treated.

Cough: Cough can be a symptom of cardiac disease, particularly heart failure. Sometimes people can wheeze as well. However, there is no such entity as a "cardiac cough" that has any specific characteristics that differentiate it from other types of cough. The whole clinical picture has to be considered.