if you can put your hand on your heart and say something, you can say it knowing that it is the truth.
I couldn't put my hand on my heart and say I'd never looked at another man.
(redirected from put hand on heart)
put (one's) hand on (one's) heart
To swear that something is completely truthful, genuine, or sincere. I can put my hand on my heart and say that we have only ever acted in the best interests of our customers.