Unheeded describes advice, a warning, a request or a rule that people did notice — they saw it, they heard it — and then did nothing about. That is what makes it sharper than unheard. Unheard can mean the message never arrived; unheeded means it arrived and was ignored anyway. So this word almost always carries a quiet accusation, and very often a bad ending: the warnings went unheeded, and the bridge collapsed. Because of that, unheeded lives mostly in serious writing — news reports, history, editorials, disaster stories. In ordinary speech people just say "nobody listened" or "they ignored it". Two patterns cover nearly every real use. The first is go unheeded, sometimes pass unheeded: his advice went unheeded. The second is putting it straight after a noun as a comment: her warning, unheeded at the time, turned out to be exactly right. The thing that goes unheeded is nearly always a message of some kind — a warning, a plea, a call, advice, an appeal — not a person and not an object. You can say the warning went unheeded; you would not say the man went unheeded. The base verb heed is itself rather formal and old-fashioned, and honestly this participle is more common in modern English than the verb it came from.

被當耳邊風、置之不理的（勸告、警告）。中文常說「充耳不聞」「置若罔聞」；重點是「聽到了卻不理」，跟 unheard「根本沒被聽見」不同。