Male factor infertility as the sole cause of infertility accounts for approximately 35% of infertility cases. This diagnosis is sometimes seen in men who have a varicocele which is an enlarged vein within the left testicle. Male infertility can also occur as a result of trauma or surgery to the testicles. Recent scientific studies have also shown that in some cases of male infertility, there may be a significant genetic component which may be heritable. Despite the above causes, a significant portion of male infertility is unexplained.