Closed one's heart is the perfect antonym for the phrase 'opened one's heart.' When someone chooses to close their heart, they are resistant to sharing their thoughts, feelings, and emotions. They may choose to put up a wall between themselves and others and may be unwilling to trust, form intimate relationships or share their experiences. On the other hand, when one chooses to open their heart, they welcome the opportunity to connect with others on a deeper level, share their experiences, and express their emotions freely. In conclusion, opening one's heart requires vulnerability and a willingness to be seen, while closing one's heart reflects fear, mistrust or emotional detachment.