S1: The heart is pump of life.
P : They have even succeeded in heart transplants.
Q : Nowadays surgeons are able to stop a patients heart and carry out complicated operations.
R : A few years ago it was impossible to operate on a patient whose heart was not working properly.
S : If heart stops we die in about five minutes.
S6: All this was made possible by the invention of heart-lung machine.
The Proper sequence should be: