Chocolate contains substances called Phenylethylamine and Seratonin, both of which (put simply), are mood lifting agents found naturally in the human brain. (...) This causes rapid mood change, a rise in blood pressure and increasing heart rate, inducing those feelings of well being, bordering on euphoria usually associated with being in love. Eating chocolate also releases Phenylethylamine and Seratonin into the system producing those same euphoric effects, plus it can give a substantial energy boost (...), so it's probably these effects which gave rise to chocolates reputation as an aphrodisiac.