His concerts abroad have always extracted flattered reviews from international famous pianists and musicologists like Roberto Szidon and Paul Badura-Skoda. One of the greatest Greek pianists of his generation Maestro Mastroyiannis has appeared as soloist with orchestras like the Slovak State Philharmonic, the Macedonian Philharmonic, the Plovdiv Philharmonic the Kiev Camerata etc. and in famous concert halls like "Ateneul Roman" in Bucharest performing a vast repertoire and many Piano Concertos less presented but of great importance.

Many invitations for performances in the USA, Ukraine, England, Netherlands, Australia and South Africa either as a recitalist, chamber-music musician or soloist with symphony orchestras to the frames of international music festivals.

Maestro Mastroyiannis performs all kinds of Piano and chamber music included first performances of new music and in general, unusual repertoire. He is an exceptional partner for singers accompanying Lieder recitals.

He is also accepting every year a number of invitations for master-classes and participation as a member of the jury in international competitions.