It would help if you posted the icon.
But you should be aware that there are a huge number of apps, as well as many different types of apps, that use heart icons. So unless it's a fairly well-known one or distinctive enough for a reverse image search to work there is a good chance that nobody will be able to recognise it. Usually the best way is to ask the other person (since most of these queries concern screenshots from someone else's phone, even more so when heart-shaped icons are involved!). But if you post it we'll give it a go.