Nothing symbolizes love more completely then the heart. And for a romantic person there is no other symbol as important as the heart. A heart signifies life and if you give your heart to someone it means to handover to her or him one's existence.
Around 12th Century people were not aware the function of heart was to circulate blood inside the human body. What they knew was that heart begins to beat faster when a person is upset or excited. They, therefore, derived that the heart was the seat of emotions and feelings.
Today, even though it has been scientifically proved that emotions come from the brain, the heart remains a powerful symbol of love and Valentine's Day.
I have given my heart to only one man.
Happy Valentine's Day
I Love You Tom Y