In a medical sense, life is determined by the sustained presence of a heartbeat.
If no heartbeat is there, then life is not there. A patient can have an absence of breath, but if a heartbeat is determined, we can breath artificially for the person. This is what a ventilator does. It is true that if there is no heartbeat we can give artificial heartbeats for a while -- this is cardiopulmonary resuscitation -- but it is not as effective as the real deal and is not sustainable.
The Scriptures tell us:
"For ye are dead, and your life is hid with Christ in God. When Christ, who is our life, shall appear, then shall ye also appear with Him in glory." (Colossians 3:3-4.)
First Paul tell us that we are dead, and then that our life is hid with Christ in God. Next he tells us that Christ is our very life. Paul is not contradicting himself here, he is teaching us that our life in this flesh is dead in it's ability to please God, in fact to do anything for God apart from the working of Christ in and through us. Then he goes on to tell us the truth of our lives is that our spirit which has been quickened, or made alive, by the Holy Spirit is presently --this very moment-- hid with Christ in God. What safer place can there ever be? Paul goes on to tell us that Christ is our very life.
Compare this with these in Galatians:
"I am crucified with Christ: nevertheless I live; yet not I, but Christ liveth in me: and the life which I now live in the flesh I live by the faith of the Son of God, who loved me, and gave Himself for me." (Galatians 2:20.)
The sacrifice of the Lord Jesus Christ was so great that when we trust and believe in Him by faith, our old heart, which was dead to God, is enlivened, created anew and now lives to serve and follow the Lord. Yet, we are still enrobed with bodies of flesh which have, as Paul called it, a law of sin. But us, the part of us that makes us who and what we are, is new. To believe that we are still wicked and evil would be like wrapping ourselves in a corpse and carrying it with us wherever we go. We would smell the stink and feel the weight, but none of that would truly be us. We must make the choice to not carry that stinky weight around and to believe what the Bible says is true of us as believers is actually true.
Let us rejoice in the complete work of salvation the Lord has done in us and look toward the day we will see the redemption of these bodies. Let us believe that the Lord has placed His Spirit in our newly created spirit and that we are indeed, "hid with Christ in God," and "created in righteousness and true holiness."
"That ye put off concerning the former conversation the old man, which is corrupt according to the deceitful lusts; And be renewed in the spirit of your mind; And that ye put on the new man, which after God is created in righteousness and true holiness."