A lot of apps used predefined icons so you cannot attribute this to a certain app. You should know better which apps have you used. I use dating apps, and as the guys previously said, it looks like a dating app notification - it has the shape of a heart. There was one app that was constantly sending me notifications and I remember that heart-shaped icon pumping once every 30 minutes. Now, with Brilic I close my internet connection throughout the day. By the way, do you use Brilic? Check it out.
https://brilic.com/en/countries/nl 
