The heart was an organ that pumped blood through the body of certain species (including humans, Kaleesh, Rodians and Umbarans) by "beating." Smaller lifeforms had a quicker heartbeat than larger ones. Some species, like Zabrak, Cereans, and Chadra-Fans, had two hearts. The Wermal species had three hearts. Skakoan hearts were in the lower region of their abdomens, therefore a shot to the upper chest was not fatal to them. Humans, on the other hand, had their hearts in their chest cavity.
When an individual became physically active, excited or ill, their heart rate could rise significantly. When a being was exposed to cold and inadequately protected, their heart rate and breathing would slow so that they became hard to detect at all. If the heart ever stopped beating completely, death ensued. Human Jedi were known to have much slower heart rates than an average human. The Rodian senator Onaconda Farr died after drinking poison that affected his heart. Physical injuries to the heart could also lead to fatal issues: the Umbaran senator Mee Deechi perished after Lolo Purs drove a dagger through his heart. Disease was another malady that could affect the heart. One illness rotted the heart of Senache and eventually killed him. Princess Breha Organa of Alderaan fell from the Alderaanian mountain Appenza Peak while completing her Challenge of the Body and almost died. As a result her heart and lungs were replaced with pulmonodes.
The word "heart" also referred to a person's personality or disposition. While fighting Alexsandr Kallus, Grand Admiral Thrawn told him that he had "the heart of a rebel." During the war between the First Order and the Resistance, Supreme Leader Snoke accused Kylo Ren of having "too much of his father's heart."