I am 40 and when I have a period it is really heavy bleeding and lots of clots? Is it serious?

Talk to your gyne. You should talk to your gynecologist. She/he would examine you and likely will order a pelvic sonogram to check on your reproductive organs. People with significant fiborids do have heavy period frequently- and that can be seen on the ultrasound. Also, you may need to tell your primary care doctor to check your blood. If bleeding significant, you may have iron deficiency anemia as well.