Many, many years ago, when I first saw a real (chicken) heart, I was surprised that it did not look at all like I thought the “real” heart should. No encyclopaedias and medical textbooks available to me then and since mentioned the “heart-shaped” hearts either. And what ♥ has to do with love? True, the heart keeps us alive, but shouldn’t there be organs a bit more directly responsible for love? It was not until I read Betty Dodson’s Sex for One that I got an explanation — mind you, not the explanation, just a hypothesis... still, way better than anything I came across before.
The geometric shape ♥ was known since antiquity but was rather associated with foliage than heart. According to Wikipedia, the first known depictions of a heart as a symbol of romantic love date to the 13th—14th centuries, but the hearts in question were shown either pine cone- or pear-shaped. Maybe those latter objects were just pears.
Various hypotheses attempted to connect the “heart shape” as it evolved in the late medieval period with instances of the geometric shape in antiquity. Such theories are modern, proposed from the 1960s onward, and they remain speculative, as no continuity between the supposed ancient predecessors and the late medieval tradition can be shown. Specific suggestions include: the shape of the seed of the silphium plant, used in ancient times as an herbal contraceptive, and stylized depictions of features of the human female body, such as the female’s buttocks, pubic mound, or spread vulva. <...> Inverted heart symbols have been used in heraldry as stylized testicles (coglioni in Italian) as in the canting arms of the Colleoni family of Milan.Whatever theory is right, I hope from now on you’d think a few moments more before investing in a T-shirt or tea mug with “I ♥ something” on it.
The red heart ♥ has been used on playing cards as a suit since the 15th century. Hearts, Herz, cœurs, corazones... In Russian, however, this suit is called черви or червы, from the adjective червонный, “red”.