The muscle layer of the heart is known as the

Myocardium

Explanation:

myo means "of muscle" or "relating to muscle"

cardium denotes tissues or cells that are associated with the heart.

The myocardium is an involuntary (we don't have to actively contract it), smooth muscle. The cells that make up the muscle are called cardiomyocytes.

These cells/tissues are hugely important for the normal functioning of the heart, and disruption is associated with diseases such as ischemic heart disease.

it can be observed without changing the identity of the object.

it depends on what substance you're talking about as well as many other factors. in quantum mechanics, the observation of particles affects the observers ability to measure certain properties. for example: you can know the velocity of a particle, but you can't know it's position; or you can know it's position, but not it's velocity. it's like trying to find out where a grain of sand is by throwing other grains of sand at it. once you find out where it is, it's been moved. it's also like trying to find an answer to the question of whether or not a tree falling in a forest makes a sound if nobody is there to hear it. paradoxically, the only way to find out is to be there and hear it.