If someone describes you as openhearted, they mean that you're kind, honest, and generous. An openhearted neighbor won't hesitate before helping you search for your lost cat.
You openhearted nature will show if you treat others with warmth and kindness. There is also an honesty and clarity associated with this adjective: "His open-hearted response when I asked him some difficult questions made it much easier to be straightforward about my own life." The idea is that your heart is open if you unreservedly share what you feel.