Why does a mutation in a sperm or egg cell have different consequences than one in a heart cell?

A sperm-egg fusion occurs when a mutation in one of the sex cells is replicated in every cell in the body. Since every cell is derived from a single sperm-egg cell, every subsequent cell that is copied from the original cell will also have the same mutation.

A mutation on a heart cell will only affect the other mutated heart cells that arise from the mutated heart cell's mitosis; it will not affect the germ or sex cells as much.

A mutation in a sperm or egg cell can be passed on to future generations because it affects the genetic material that will be inherited by offspring. On the other hand, a mutation in a heart cell usually affects only the individual in which it occurs and is not passed on to offspring. This is because mutations in somatic (non-reproductive) cells like heart cells are not transmitted to offspring during reproduction, while mutations in germ cells (sperm and egg cells) can be inherited by offspring.