Transhumanism isn't just advanced medicine. The idea isn't to replace a human heart with an artificial heart that's mostly functionally identical (current-day technology). The whole idea is to transcend biological limits using technology, i.e. develop eyes, ears, and brains that are functionally different and superior.

Prolonging human longevity is just one of the (many) goals of the transhumanist movement). Its core definition (according to Oxford dictionary) is: "the belief or theory that the human race can evolve beyond its current physical and mental limitations, especially by means of science and technology."

The original transhumanist dream was that we would each gain more control over our biology (that sounds like freedom to me); the realities of today's world mean that we would instead gain marginally more control, while corporations and governments gain exponentially more control (that sounds like tyranny to me).