Dr. Isis explains why the absence of female test subjects is not simply a matter of gender discrimination.
Namely, beliefs about gender have most certainly had a role in female-blindness (unlike gender-blindness, that's when researchers who depend on women to staff their offices--and who may themselves be women--don't notice that their research subjects are not). This can account, in part, for the assumption through most of the twentieth century that heart disease progresses the same in women as in men. The underlying assumption was that the differences between men and women are just the sexy ones. Although we know better now, research on women still progresses more slowly, and when research on women is lacking, the default position is that they must be more-or-less like men.
Dr. Isis says:
"as we interpret published findings, especially as they apply to the treatment of human patients, we have to remember to ask who comprised the cohort and ask if it is appropriate to apply the findings to female patients. Finally, we have to continue to support groups like the Society for Women's Health Research that remind us of a major gap in medical knowledge, appreciate the effect this gap has on public health, and aims to close it."