The pathology of the heart is Excess Joy. Imagine that, excess joy, who doesn't need more of that?
Excess joy really looks like anxiety or other emotions reflected into the heart, mind, that have been stirring around for a longer time than needed. Emotions, in a state of health, are experienced and moved through without becoming locked in that state. In Chinese Medicine all emotions are reflected up through the heart, spirit, or shen. It's problematic when you are unable to get off the roller coaster. One of my clients described it as feeling like having too many tabs and windows open in your mind, essentially taking up head space.
Joy in the appropriate state is the ability to connect with others and stay present in the moment. The heart in Chinese Medicine is considered the emperor of body, mind, and spirit. The vessel itself is hollow meant to conduct and house the spirit. In health it allows us to be present and flexible/adaptable to our surroundings simultaneously.
In health it allows us to experience life without checking out, or disconnecting.