In chapter 9 Dimesdale's health begings to fail. What is he seen doing "on any slight alarm or other sudden accident"?

He would put his hand over his heart,

"By those best acquainted with his habits, the paleness of the young minister’s cheek was accounted for by his too earnest devotion to study....his voice, though still rich and sweet, had a certain melancholy prophecy of decay in it; he was often observed, on any slight alarm or other sudden accident, to put his hand over his heart, with first a flush and then a paleness, indicative of pain."