Heart

Throughout Castlevania games, hearts have often served as ammunition for the various sub-weapons. In games without hearts or subweapons, they can replenish the player's magic meter instead.

Throughout the series, there have been many heart-based items, such as the regular heart, which restores 1 Heart Point, large hearts which restore 5, and in some cases, even the Heart Refresh, an item which restores all hearts, akin to Mana Prism. However, hearts are not the only way to increase a players heart points.

Standard Heart Restoration
Hearts are usually restored in one of the following ways;

Small Hearts
Small Hearts are the most common restorative item in the Castlevania series, found in a myriad of places ranging from enemies to candles. They usually replenish a single heart in your heart meter. A single heart isn't much, however, some weapons only require a single heart in order to activate, such as the dagger.

Large Hearts
Large Hearts usually restore 5 hearts for a player, and are most often found in candles. They are usually kept around the middle of an area, however some instances, they are right next to an entry, making them easy to collect before a boss fight.

Heart Refresh
Heart Refresh in Castlevania: Symphony of the Night takes the appearance of an Angel holding onto a heart, and restores 500 hearts. This is particularly useful during longer boss fights.

Heart Container
Increases the maximum Heart Points, and is also worth about 5 hearts. Usually found after bosses or in areas which require a special means to access.

Castlevania II: Simon's Quest
In this game, hearts are still found by killing enemies, but they are used as currency to buy things from the hooded shopkeepers.

Castlevania: The Adventure
Heart is an item found in Castlevania: The Adventure, found in candles. Unlike other Castlevania games, the heart recovers Christopher Belmont's health.

Flashing Heart will completely fill Christopher's energy bar, though they are more rare than regular Heart items. These are usually found in hidden rooms, though some will appear out in the open.

Alternate Methods
Collecting Hearts isn't the only way in which to restore them. in Symphony of the Night there also includes special equipment with heart restoration effects;

Blood Cloak
Restores hearts equal to the damage taken. This is an easy way to quickly increase Hearts if you plan to defeat a boss with only a sub weapon

Alucard Shield Spell
When the Shield Rod is combined with the Alucard Shield, the resulting spell can inflict 255 damage repeatedly, as well as restoring 8 HP and 1 Heart per hit. Can be used on Stone Skulls until MP is completely drained.

Herald Shield
Using the Herald Shield to block a projectile will give you 1 heart. The best way to use the Herald Shield for obtaining hearts is the monster Tin Man.