He might well have smote it!

(John MacDuff, "The Sure Ground of the Believer's Expectations" 1859)

"But the tax collector stood at a distance. He would not even look up to heaven, but beat his chest and said: God, have mercy on me, a sinner!" Luke 18:13

Not merely was it on his heart that the burden of guilt lay with an oppressive weight, but out of it had come all that was sinful in his outward conduct. His heart was . . .
  the storehouse from which the evil treasures had been brought forth,
  the poisonous fountain from whence the various streams of pollution flow,
  the heaving volcano from which the infernal lava in devastating torrents had emanated.

He might well have smote it, being fully assured that the abounding sinfulness of his life could be traced to the inherent corruption and desperate wickedness of his heart.

"I tell you that this man, rather than the other, went home justified before God. For everyone who exalts himself will be humbled, and he who humbles himself will be exalted." Luke 18:14

It is just so with every true penitent. The infinite perfection of the divine character, in contrast with his own filthiness, covers him with confusion, so that he is compelled to cry with Ezra of old, "O my God, I am too ashamed and humiliated to lift up my face to You!" Ezra 9:6