Three Hearts and Three Lions is a 1961 fantasy novel by Poul Anderson, expanded from a 1953 novella by Anderson which appeared in Fantasy & Science Fiction.
Francis Morgan, a wealthy heir of industrialist and Wall Street maven Richard Henry Morgan, is a jaded young New Yorker. When his father's business partner Thomas Regan suggests that Francis take a holiday in Central America, ostensibly to search for the treasure of the Morgans' legendary ancestor, Francis thinks it's a splendid idea. But he never suspects what adventures await across the border...
Meanwhile, back in New York, a cunning enemy is positioning himself to destroy the Morgan fortune. Francis must get back in time to thwart the takeover and save his family's business