Your heart has always been open.
Your heart is and has always been open.
Your thoughts, how you perceive and interpret sensory input (also your thoughts), and the degree to which your nervous system is activated (triggered by what you think and how you perceive, both consciously and not, both verbally and pre-verbally) are what prevent you from experiencing this truth.
It's about where you place your attention. When your attention is on your limiting interpretation of your experience rather than on direct experience, you become myopic toward the barrier, like the fly who unrelentingly beats up against a closed window, unaware that it is open only 10cm away.
The reason our language matters so much is because if you tell yourself you need to "open your heart" you will inadvertently put your attention on the wrong thing, just like that fly. This creates unnecessary confusion, complication, and diversion from what is true. It also results in a pushing and pulling to blast open the heart through peak experiences when the problem has nothing to do with the heart in the first place at all.
Your heart is just fine. It has never been closed; it is your mind which is closed. It's no one's fault that this is the case, it's just how it is. This is or has been true for most of us.
We must challenge the way we think, and how we perceive. We must work to calm the nervous system and learn to self-regulate and discern with whom we co-regulate (ie: healthy boundaries). These are essential life skills which bring spiritual and emotional maturity.
When we LIVE these ways of being consistently we realize our heart has been open all along, and, what's more is that from there we discover an endless well of wisdom and energy that allows us to live in the world actualized as open-hearted beings.