Heartless means cruel and completely lacking in sympathy or kindness. A heartless person does mean things without caring about how others feel. When the villain in a story throws someone out into a snowstorm without a coat, that's a heartless act. When someone mocks a classmate who's already upset, they're being heartless.

The word suggests more than ordinary meanness. Someone might be rude or thoughtless without being heartless, but a heartless person seems to have no compassion at all, as if their heart were missing. Think of Ebenezer Scrooge in A Christmas Carol refusing to help the poor at Christmas, or Cruella de Vil wanting to harm puppies for fashion. These characters act heartless because they care only about themselves and ignore the suffering they cause.

You might hear someone say “How could you be so heartless?” when they're shocked by cruel behavior. The word carries real weight: calling someone heartless is a serious accusation. It means they've done something that makes others question whether they have any kindness inside them at all. Fortunately, even characters who seem heartless can sometimes change, like Scrooge learning to care about others, which is why his transformation feels so powerful.