At the end of its period the main sequence of a very heavy star is?

Not quite sure what you mean by this question but the formation and main sequence of most stars is pretty much the same but the 'end' of a star can be quite different depending on the stars mass. A heavy star, towards the end of it's life, will start producing the heavier elements within it's core until it gets to a point where it can no longer sustain itself. At this point the star will go supernova violently blowing off it's outer layers far into space and, for a short time, it can briefly outshine the galaxy the star is in!