The long plateau phase of the cardiac muscle action potential is due to

The Cardiac Muscle

Explanation:

The long plateau phase of the cardiac muscle action potential is due to Calcium channels remaining open.Depolarization is trailed by the plateau phase wherein film potential decreases generally gradually. This is expected in enormous part to the opening of the moderate Ca2+ channels, permitting Ca2+ to enter the cell while few K+ channels are open, permitting K+ to leave the cell.  During stage 1, there is halfway repolarization, in view of an abatement in sodium porousness. Stage 2 is the plateau phase  of the cardiovascular activity potential. Film penetrability to calcium increments during this stage, keeping up depolarization and dragging out the activity potential.

Artificial Selection is the the process of taking 2 organisms (plants/animals) with desirable traits, or traits they want in future generations, and breeding them together.

Natural Selection is NOT correct because it does not apply to the question. Respectfully, you can look at Natural Selection as "Survival of the Fittest" (Explained by Charles Darwin), the organisms that adapt and overcome harsh conditions in their environment live on to produce more offspring that are ALSO adapted to the environment.

Variation also is NOT correct because Artificial Selection actually decreases the chances of variation in the future.

Mutation is when a new DNA sequence is created for a certain/specific gene, making a new allele. However, mutation is mainly caused by environmental factors, such as Ultraviolet radiation from the Sun.

In conclusion, the process described in the question is called "Artificial Selection."