All major credit cards, Visa, Master Card, AMEX and etc. are accepted in the biggest shops and all banks in Bulgaria.
In 1997 the Bulgarian LEV was pegged to the Euro at an exchange rate of 1 EURO = 1.96 LEV, this rate never changes.
When looking to exchange Euros into levs, it is advisable to look for a place where for 1 EURO they will give around 1.95 LEVS.
Be very careful when exchanging currency - quite often actual exchange rate is lower than the rate advertised rate on the front of the exchange office - always ask the what the rate is before exchanging any money.