His heart
leb (labe)
the heart; also used (figuratively) very widely for the feelings, the will and even the intellect
is as firm
yatsaq (yaw-tsak')
cast, cleave fast, be (as) firm, grow, be hard, lay out, molten, overflow, pour (out), run out, set down, stedfast.
as a stone
'eben (eh'-ben)
a stone -- + carbuncle, + mason, + plummet, (chalk-, hail-, head-, sling-)stone(-ny), (divers) weight(-s).
yea as hard
yatsaq (yaw-tsak')
cast, cleave fast, be (as) firm, grow, be hard, lay out, molten, overflow, pour (out), run out, set down, stedfast.
as a piece
pelach (peh'-lakh)
a slice -- piece.
of the nether
tachtiy (takh-tee')
lowermost; as noun (feminine plural) the depths (figuratively, a pit, the womb) -- low (parts, -er, -er parts, -est), nether (part).
millstone