The point is, you have applied an arbitrary standard to the word "dead" and it has nothing to do with biological fact. I can make any word mean anything I want it to! That doesn't change what is factual! We could say that someone is "dead" if they don't pass a physical or an IQ test, if we wanted to make that the definition, but it has nothing to do with reality, it is our arbitrary definition and nothing more.
Yes, the fact that we have the technology to keep a heart beating eternally, is a determining factor in why we have to establish some other criteria. If we didn't, we could say that people can live forever with the aid of a machine. A human can't survive without a functioning heart, just as they can't survive without a functioning brain. We don't have the technology to keep a brain operating, if we did, the debate of "death" might be different.
Whether we can use technology to keep an organ functioning, has nothing to do with what is living and what is dead. A zygote doesn't need a brain to be considered a living human organism, that is a matter of biological fact, regardless of what arbitrary definition we have applied. You are trying to take an arbitrary definition we've established for death, and apply it to life, and it is a dishonest approach which denies science and biology.