。
I talked to my heart's content.
Literal
I [topic-は] heart-satisfied [until-まで] conversation [object-を] did
心ゆくまで = 'until the heart is satisfied' = 'to one's heart's content.' A literary expression: 心 (heart) + ゆく (archaic for 行く, to go/proceed) + まで (until). Carries a quietly poetic ring, common in literary prose.