Why are vampires depicted as only being able to be killed by a wooden stake through their hearts?

Driving a wooden stake through a vampire's heart is the most popular way of killing them. Many stories depict alternatives as being available or required. For example, in the book Dracula, a wooden stake can only paralyse the vampire, not kill them; to kill them their head should is cut off. Several other pieces of literature depict various methods of killing a vampire, including burning, exposing them to sunlight, forcing them to drink holy water, etc.
because people say that the only thing keeping vampires alive is their connection of their heart and brain and without one of them they will be destroyedbut also vampires can be killed by being caught in the sunlight.