Eight shapes, from three different runs of the standard

Ask Unicode for every character in the Basic Multilingual Plane whose official name contains HEART and eleven come back. Three of them are CJK radical characters that are named for the heart radical and are not heart-shaped at all; they are handled on tiny heart symbols, where their width matters. The other eight are the heart shapes, and they come from three separate places.

The suit pair

U+2661 WHITE HEART SUIT and U+2665 BLACK HEART SUIT belong to the run of eight playing-card suits. WHITE and BLACK are Unicode's words for hollow and filled; neither says anything about colour, and nothing in either character makes it red. Both carry East Asian Width Ambiguous, which the other six do not. The rest of that run is the other three suits, in the same two fills, on card suit symbols.

The two ornaments

U+2764 HEAVY BLACK HEART is the bare heart: no stem, no leaves, nothing attached. It is the one to reach for when you want a heart and only a heart. U+2763 HEAVY HEART EXCLAMATION MARK ORNAMENT looks like a near-twin in a list but is not a heart on its own — read the end of its name. It is an exclamation mark, with a heart in place of the upper stroke and the dot still sitting underneath. Paste it after a word and you have punctuated the sentence.

The four bullets

U+2766 FLORAL HEART, U+2767 ROTATED FLORAL HEART BULLET, U+2765 ROTATED HEAVY BLACK HEART BULLET and U+2619 REVERSED ROTATED FLORAL HEART BULLET are ornaments meant to sit in a line of text as a marker. Three of the four names contain ROTATED, and that is the whole difference: the heart is lying on its side rather than standing on its point.

The sideways heart is one of three characters

❥ is the plain filled heart turned onto its side. ❧ is the foliate version turned the same way, and ☙ is that one mirrored — its name carries both REVERSED and ROTATED. If you want a heart lying down, pick by whether you want leaves and which way it should face; there is no separate "sideways heart" character beyond these.

What eight characters cannot give you

There is no blue, purple, broken or sparkling heart here. Those are separate characters outside the Basic Multilingual Plane and are not in this set. There is no big or small heart either: size is not a property of a character, it comes from the font size around it and from whether the character is being drawn in its emoji form.

U+2661 and U+2665 being Ambiguous width is the practical difference between the suit pair and the ornaments. Ambiguous means the cell count depends on the font context: narrow in a Western one, full-cell where East Asian text is expected. If a heart is arriving larger than the text around it, or a monospace column refuses to line up, the tiny heart page linked above works through both causes. To put one into HTML, a form field or anything ASCII-only, see heart symbol in text and HTML, and for the filled-against-hollow question on its own there is black and white heart symbols. All of it sits under symbols to copy and paste.