It implies that something was said or done but was not noticed or acted upon.
Here are some examples:
* "Her warnings went unheeded, and the disaster struck."
* "His pleas for help were unheeded, and he was left to fend for himself."
* "The signs were there, but they were unheeded."
The word "unheeded" often carries a sense of consequence or regret, as the ignored warning or plea often leads to a negative outcome.