How is the dragon in Beowulf killed?

Beowulf was very old but he hasn´t lost physical skill and cunning so he rode the dragon for some minutes then when the dragon attacked the king and his concubine he found the heart of the dragon it was in his throat, beowulf tried to cut the monster´s heart with his sWord but suddenly he lost it that´s when he decided to cut one of his arm to get the chance to extract the heart by his own hands and he did it but he couldn't stay alive he died with the dragon.