Good-heartedly, a commonly used adverb that describes the sincerity of one's actions, can have various antonyms. These include actions or behaviors that are insincere, malicious, selfish, or callous. Words such as selfishly, maliciously, unkindly, cruelly, heartlessly, and insincerely are antonyms that indicate the opposite of good-heartedness. One may act selfishly by putting their interests or desires before others, while acting maliciously, cruelly, or heartlessly implies causing harm or pain intentionally. Finally, being insincere suggests that one's actions are motivated by hidden agendas or dishonesty, rather than being genuinely good-hearted. In summary, antonyms for good-heartedly are actions and behaviors that are insincere or motivated by negative intentions.