There is much debate as to when life "begins"... is it at conception? a few days after.. at one's exiting of the womb etc... But there is also debate as to when one is actually "dead." Is it when your heart stops? When your brainwaves cease? Is it when breathing ceases? etc...
In order to define when each of these events occur, one must also have a firm definition of what "alive" actually means.
Differing medical and political views of when someone is really dead are prevalent throughout the world.
Rigor Mortis is the temporary fixation of muscle tissues brought on by the ...... oh heck... isn't this post about valve adjustment?
So, picture yourself locked in a very small room, not much bigger than your body, with a small supply of food and air to breathe, but nowhere is a toilet to be seen. You can eat your food until it runs out and starve to "death", and breathe until you run out of air and asphyxiate, and poop until you have no space to poop anymore. This is basically what happens to your individual cells in your body once circulation ceases.
You = a single cell, say perhaps a muscle cell.
Your very small room = the space your cell occupies plus a bit of interstitial fluids surrounding you.
Your food = nutrients brought to you by blood circulation
Your air to breathe = brought to you in the blood that feeds you and what you exhale is taken away by the blood too.
Your toilet = your interstitial fluids are the septic system, the plumbing is your lymphatic system.
Your poop = not removed as your lymphatic system which drains into your blood, and gets filtered out by the liver and kidneys isn't running anymore. The poop you as a cell produce causes your cell and your neighbours to all stiffen up for lack of space. But then after a while of this, someone comes along, namely digestive enzymes, and change your poop and also eat your cell walls allowing you to relax.
While you are stuck in this room, the reason you, as a cell, are not receiving proper food, air and toilet facilities is because your heart has stopped. But wait... your heart stopped? You stopped breathing? But as a cell.... you are still alive... but you've been pronounced as "dead"
See the confusion?
Oh, and to bring this back on topic.... There are valves in the heart.
Mitral, tricuspid, pulmonary and aortic... doctors are often required to adjust these valves if not in tolerance.