What does a cardiac cough sound like?

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.
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.