With your hand on your heart - Idioms by The Free Dictionary
with your hand on your heart
with (one's) hand on (one's) heart
Giving the assurance or impression that one is being completely truthful, genuine, or sincere. With my hand on my heart, I can say that we have only ever acted in the best interests of our customers. She stood their with her hand on her heart and lied to our faces.
with your ˌhand on your ˈheart,
ˌhand on ˈheart speaking very honestly and telling the truth: I can tell you, hand on my heart, that I never took any money out of your purse. ♢ How can you stand there with your hand on your heart and tell me that?