

Simulation based on:

Area of circle: A=Pi*r^2

Area of myocardial circle: Am=Pi*ro^2 - Pi*ri^2
where ri=inner radius and ro=outer radius.

In pumping heart, the muscle area stays the same,
but radius changes. Thus, if new inner radius is ri2,
the new outer radius ro2 can be calculated:

Am = Pi*ro^2 - Pi*ri^2 = Pi*ro2^2 - Pi*ri2^2
<=>
ro^2 - ri^2 = ro2^2 - ri2^2
<=>
ro2^2 = ro^2 - ri^2 + ri2^2

or new inner radius:

ri2^2 = ro2^2 - ro^2 + ri^2
