According to Olivander, as a rule, dragon heartstrings produce wands with the most power, and which are capable of the most flamboyant spells, as well as it tends to be easiest to turn to the Dark Arts, but is equally good at defense against them, so he should not worry too much. It is also the most prone of the three cores to accidents, being somewhat temperamental, that is why the carefulness during casting is highly recommended. 