At the deepest level, an 'open heart' is spacious presence, in which the sense of separateness between yourself and the 'other' dissolves and there is the recognition of oneness, of shared consciousness. That recognition is love. Sensing the formless essence in another and recognizing it as one with your own essence - that's what love is. All this is an intrinsic part of the awakened consciousness and the revelation of the spiritual dimension of life.