cross my heart (and hope to die)

US /krɔs maɪ hɑrt (ænd hoʊp tu daɪ)/
UK /krɔs maɪ hɑrt (ænd hoʊp tu daɪ)/
"cross my heart (and hope to die)" picture
1.

我发誓, 千真万确

used to emphasize that one is telling the truth or making a sincere promise

:
I promise I won't tell anyone, cross my heart.
我保证不会告诉任何人,我发誓
He said he'd be there on time, cross his heart and hope to die.
他说他会准时到,他发誓