Despite the risk to women from heart disease, nearly all randomized, controlled studies on risk factors, treatment, and outcomes of cardiovascular disease have exclusively involved men, and extrapolation of those findings to women has resulted in several misinterpretations. More recent studies that controlled for different age and risk factors in women found that women have tended to be referred for angiography, coronary artery bypass graft surgery, and angioplasty significantly less often than men. A gender bias may contribute to the lower referral rate for women.