House Targaryen’s sigil is a three-headed dragon that breaths red on black flames. The 3-headed dragon symbolizes the conqueror and his two sisters who were named Rhaenys and Visenya. The words of their house were fire and blood. Even though the Targaryen kings seized their place at King’s Landing, Dragonstone continued as the traditional seat of the heir-apparent to the throne. He was recognized as the Prince of Dragonstone. Any younger siblings of the Prince of Dragonstone could be summer hall and be called the Prince of Summer hall.
From historical times, House Targaryen always followed the gods of Valyria. A short while before the Seven Kingdoms were conquered, the Targeryens deserted the Valyrian gods and moved to the faith of the seven which dominated the region of Westeros. They however continued to follow some of the Valyrian practices such as marriage between brother and sister, aunt to nephew, cousin to cousin and uncle to niece.
The title of ‘blood of the dragon’ referred to what was considered classic Targaryen features which were silvery-golden hair and purple eyes. Although the Targeryens are in no way immune to heat, they are known to tolerate more heat than most of the ordinary people.
The Targeryens are as dragon lords and are always closer to dragons than any other men. Aegon I initiated dragons to the land of Westeros when he first conquered it, and the dragons were reserved and ridden by the Targeryens until the final one perished in the reign of Aegon III the Dragon Bane.
So the Targeryens kept dragons for most of their reign in Seven Kingdoms. They housed them by building a massive domed structure in the King’s Landing that was called the Dragon pit. They bred new dragons from the original three of Aegon that were called Vhagar, Meraxes, and the feared Balerion.
Nonetheless, there were violent deaths in battle and a growing infirmity in each generation that led to the dwindling of the family stable. The last of the Targaryen dragons was a sterile and deformed creature that died at a very young age. It has never been clear what eventually caused the last dragons to die out. There is a legend that says that Aegon 111 had them all poisoned, but the Arch master Marwyn hinted that the Maesters might have been responsible. Other sources claimed that bringing up dragons in an enclosed space such as the dragon pit was unnatural, and it ended up stunting their growth leading to their termination.