put (your) hand on (your) heart - if you can put your hand on your heart and say something, you can say it knowing that it is the truth.

Are you telling me, hand on heart, that you have never read anyone's private mail?

• pearly gates
• pecking order
• pedal to the metal
• peel off
• peeping Tom
• pell-mell
• penchant for
• penchant for something
• pencil in
• pencil someone in
• pencil something in
• pen is mightier than the sword.
• penny ante
• penny drops
• penny for your thoughts.
• penny for your thoughts
• penny saved is a penny earned.
• penny wise and pound foolish
• pen pusher
• pen pushing
• People who live in glass houses .
• People who live in glass houses shouldn't throw stones.
• pep someone up
• pep something up
• pep talk