The new single from Demi Lovato premiered earlier this week and it has already shot to No.1 in an impressive 9 countries on iTunes.

The track, entitled 'Heart Attack', was originally intended to make its debut on March 4, but hit the web prematurely so has since been released and the reaction to it has been overwhelming.

Writing on her official Twitter page in the early hours of this morning (February 26), Lovato expressed her excitement at the song's initial success: "14 hours after releasing my new single.... YOU MADE IT #1 ON iTUNES IN 9 DIFFERENT COUNTRIES INCLUDING THE USA!!!!!!!!!!!!!!!! AHHHHH!!!"

It's still at No.1 on the U.S. iTunes chart and has beaten the likes of 'When I Was Your Man' by Bruno Mars (No.2), Adele's 'Skyfall' (No.4), and 'I Knew You Were Trouble' by Taylor Swift at No.6.

She later returned to the social networking site and added: "THIS IS ONE OF THE BEST DAYS OF MY LIFE!!!!!!!!!! ALL BECAUSE OF YOU GUYS!!!!!!!!! THANK YOU!!!!!!!!!"

Listen to 'Heart Attack' in full below: