Whither has your artful tongue lured my unguarded heart?

Tears of reckless folly fled away, before these wholesome lessons of experience were forced upon Algernon's unguarded heart.

He had allowed himself to be betrayed into no folly by an unguarded heart; no youthful indiscretion had marred his prospects.

Cleopatra was my favorite cocker spaniel, and any faint impression my fair neighbor may have made on my unguarded heart was immediately dispelled.