The heart symbol is an ideograph used to express the idea of the "heart" in its metaphorical or symbolic sense. Represented by an anatomically inaccurate shape, the heart symbol is often used to represent the center of emotion, including affection and love, especially romantic love. While ancient antecedents may exist, this shape for the heart became fixed in Europe in the middle ages. It is sometimes accompanied or superseded by a "wounded heart" symbol, depicted as a heart symbol pierced with an arrow, indicating lovesickness, or as a "broken" heart symbol in two or more pieces, indicating heartbreak.

Peepal leaves were used in artistic depictions by the Indus Valley civilisation: a heart-shaped pendant originating from there has been discovered and is now exhibited in the National Museum of India. In the 5th–6th century BC, the heart shape was used in the Roman world to represent the seeds of the plant silphium, a plant possibly used as a contraceptive and an aphrodisiac. Silver coins from Cyrene of the 5th–6th century BC bear a similar design, sometimes accompanied by a silphium plant and is understood to represent its seed or fruit.

Since ancient times in Japan, the heart symbol has been called Inome (猪目), meaning the eye of a wild boar, and it has the meaning of warding off evil spirits. The decorations are used to decorate Shinto shrines, Buddhist temples, castles, and weapons. The oldest examples of this pattern are seen in some of the Japanese original tsuba (sword guard) of the style called toran gata tsuba (lit., inverted egg shaped tsuba) that were attached to swords from the sixth to seventh centuries, and part of the tsuba was hollowed out in the shape of a heart symbol.

The combination of the heart shape and its use within the heart metaphor was developed in the end of the Middle Ages, although the shape has been used in many ancient epigraphy monuments and texts. With possible early examples or direct predecessors in the 13th to 14th century, the familiar symbol of the heart representing love developed in the 15th century, and became popular in Europe during the 16th.

Before the 14th century, the heart shape was not associated with the meaning of the heart metaphor. The geometric shape itself is found in much earlier sources, but in such instances does not depict a heart, but typically foliage: in examples from antiquity fig leaves, and in medieval iconography and heraldry, typically the leaves of ivy and of the water-lily.

The first known depiction of a heart as a symbol of romantic love dates to the 1250s. It occurs in a miniature decorating a capital 'S' in a manuscript of the French Roman de la poire. In the miniature, a kneeling lover (or more precisely, an allegory of the lover's "sweet gaze" or doux regard) offers his heart to a damsel. The heart here resembles a pine cone (held "upside down", the point facing upward), in accord with medieval anatomical descriptions. However, in this miniature, what suggests a heart shape is only the result of a lover's finger superimposed on an object; the full shape outline of the object is partly hidden, and, therefore unknown. Moreover, the French title of the manuscript that features the miniature translates into "Novel of the pear" in English. Thus the heart-shaped object would be a pear; the conclusion that a pear represents a heart is dubious. Opinions, therefore, differ over this being the first depiction of a heart as a symbol of romantic love.

Giotto in his 1305 painting in the Scrovegni Chapel (Padua) shows an allegory of charity (caritas) handing her heart to Jesus Christ. This heart is also depicted in the pine cone shape based on anatomical descriptions of the day (still held "upside down"). Giotto's painting exerted considerable influence on later painters, and the motive of Caritas offering a heart is shown by Taddeo Gaddi in Santa Croce, by Andrea Pisano on the bronze door of the south porch of the Florence Baptistery (c. 1337), by Ambrogio Lorenzetti in the Palazzo Publico in Siena (c. 1340) and by Andrea da Firenze in Santa Maria Novella in Florence (c. 1365). The convention of showing the heart point upward switches in the late 14th century and becomes rare in the first half of the 15th century.

The "scalloped" shape of the now-familiar heart symbol, with a dent in its base, arises in the early 14th century, at first only lightly dented, as in the miniatures in Francesco da Barberino's Documenti d'amore (before 1320). A slightly later example with a more pronounced dent is found in a manuscript from the Cistercian monastery in Brussels. The convention of showing a dent at the base of the heart thus spread at about the same time as the convention of showing the heart with its point downward. The modern indented red heart has been used on playing cards since the late 15th century.