I found this theme incredibly difficult. All I could find were hearts without flowers and flowers without hearts., and none were anything to do with romance or Valentine's Day. Here are my slim pickings:
By happy coincidence, a card with hearts on was sent from Belgium with a flower stamp but if you examine the postmark you will see it was sent in August, so nothing at all to do with Valentine's Day.
A card from Thailand has a heart shaped stamp. The little hearts around the edge of the stamp are gold and shine. No flowers in sight so here are a couple of flowery stamps from other countries:
Sweet peas are one of my favourite flowers. I don't know the South African flower but it's an attractive stamp.
This is a post for Sunday Stamps, now hosted by Violet Sky at "See it on a Postcard!"