Dimmsdale has begun a new habit that we might perhaps see today when someone has a heart-attack. He puts his hand over his heart, in the same place that Hester's scarlet 'A' makes its home. This is significant for a variety of reasons. First, his act with Hester and the lie about it that has continued has been figuratively and literally killing him. Second, it is the common location for both sinners. Third, this location being over the heart demonstrates that their sin is of the heart. It is an intentional sin that is going unconfessed. Sexual sin is extreme because it is personal. Letting this sin go unaddressed has caused a hurting heart for both partners because forgiveness is the only release for such sin.