"Heart" (stylized as "♥" in Fox's video preview materials) is the thirteenth episode of the third season of the American musical television series Glee, and the 57th overall. Written by Ali Adler and directed by co-creator Brad Falchuk, the episode aired on Fox in the United States on February 14, 2012, and features Valentine's Day love songs performed by the McKinley High glee club. It also features the debuts of special guest stars Jeff Goldblum and Brian Stokes Mitchell as Rachel's two fathers and The Glee Project winner Samuel Larsen as transfer student Joe Hart.

Whitney Houston's version of Dolly Parton's "I Will Always Love You" is performed by Mercedes (Amber Riley) in the episode, and the completed episode had been delivered to the network and was scheduled to run in three days when Houston died unexpectedly on February 11, 2012; a dedication to her was added in the episode's end credits. Reviewers gave Riley's rendition a very positive reception, the best of those given to the ten songs that were heard in the episode, though the performances in general were well received. It was one of only two songs from the episode to chart on the Billboard Hot 100 and the Canadian Hot 100, along with "Stereo Hearts", while the other six singles did not chart.

The heart is a myogenic muscular organ found in all animals with a circulatory system (including all vertebrates), which pumps blood throughout the blood vessels by repeated, rhythmic contractions. The term cardiac (as in cardiology) means "related to the heart" and comes from the Greek καρδιά, kardia, for "heart".

The vertebrate heart is principally composed of cardiac muscle and connective tissue. Cardiac muscle is an involuntary striated muscle tissue found only in this organ and responsible for the ability of the heart to pump blood. The average human heart, beating at 72 beats per minute, will beat approximately 2.5 billion times during an average 66 year lifespan. It weighs approximately 250 to 300 grams (9 to 11 oz) in females and 300 to 350 grams (11 to 12 oz) in males.

In invertebrates that possess a circulatory system, the heart is typically a tube or small sac and pumps fluid that contains water and nutrients such as proteins, fats, and sugars. In insects, the "heart" is often called the dorsal tube and insect "blood" is almost always not oxygenated since they usually respirate (breathe) directly from their body surfaces (internal and external) to air. However, the hearts of some other arthropods (including spiders and crustaceans such as crabs and shrimp) and some other animals pump hemolymph, which contains the copper-based protein hemocyanin as an oxygen transporter similar to the iron-based hemoglobin in red blood cells found in vertebrates.

Glee may refer to: