who came up with the shape of a heart

The origin of the heart shape we know today isn’t attributed to a single person. It evolved over time:

Possible Early Inspiration (13th Century): Some believe the shape might have been influenced by the silhouette of the silphium plant, used in ancient medicine [Source].

Early Depictions (13th-14th Century): The first known visual depiction of a heart-like symbol as a symbol of love appeared in a 13th-century French manuscript, but it resembled a pine cone more than the modern heart [Source].

Gradual Refinement (14th Century): The familiar heart shape with a base indentation seems to have emerged in the 14th century. Italian writings and artwork from this period show this evolving form