Typically that organ is your heart. It contracts and relaxes 72 times per minute, day and night, till your death. That means for hundred years.
heart
muscles
Smooth muscles
The diaphram!!
Diastolic and systolic is when your heart contracts and relaxes.
When the bicep contracts, the tricep relaxes. These pair of muscles are known as antagonists which means as one contracts, the other relaxes and vice versa.
When lowering arm biceps relax and triceps contracts. When one contracts the other relaxes when you move it forward and downward.
It Contracts
It relaxes
The heart
contracts - for antagonistic muscle pairs e.g. muscles in arm (when one relaxes, other contracts, and vice versa)
The bicep muscle. The tricep contracts to straighten the arm as the bicep relaxes.