Answer: 41390
Explanation:
I noticed that there are numbers hidden in the messages on the hearts. There is a 4 on the first heart, Me + You 4Ever. Then there is a 1 hidden in Sm1le. Next is You Make My H3art Grow Bigger. There is a 3 hidden in Heart, then Happy Valenines Day. There is the word nine hidden in Valentines. And Love was the most confusing, but then I realized that there is a 0 in Love but it was hidden because they were all uppercase.