My 16-year-old daughter has SVT and I believe that it is related to her periods, especially since it seemed to have started right around the same time as her periods about a year and a half ago. They seem to be worse and more frequent when she is late especially. Her cardiologist doesn't seem to agree that it could be hormonal though. She also has pretty significant mood issues, bleeding, and cramps. I'm wondering if it would be wise to see an Gynecologist and talk about birth control to regulate her hormones. As a side note, I also had SVT when I was pregnant with each of my children and had significant cramps, bleeding, and mood swings...but I never had the arrhythmia it at any other time.