To one's (or your) heart's content means to one's complete inner satisfaction - until one's heart is content.
This phrase is first put into print in Shakespeare's plays and there's every reason to believe that he coined it. He used it in at least two plays:
Henry VI, Part II, 1592 - Her grace in Speech, Makes me from Wondring, fall to Weeping ioyes, Such is the Fulnesse of my hearts content.
The Merchant of Venice, 1596 - I wish your Ladiship all hearts content.
It is also found in a letter Shakespeare sent to the Earl of Southampton, as the dedication of the poem Venus and Adonis:
Right Honourable, - I know not how I shall offend in dedicating my unpolished lines to your Lordship, nor how the world will censure me for choosing so strong a prop to support so weak a burthen: only, if your Honour seem but pleased, I account myself highly praised, and vow to take advantage of all idle hours, till I have honoured you with some graver labour. But, if the first heir of my invention prove deformed, I shall be sorry it had so noble a godfather, and never after ear so barren a land, for fear it yield me still so bad a harvest. I leave it to your honourable survey, and your Honour to your heart's content; which I wish may always answer your own wish, and the world's hopeful expectation,
See other phrases and sayings from Shakespeare.