Answer: The correct answer is- Heart will not function properly.
Mutation can be described as permanent change in the genetic material ( that is DNA) of living organisms. If mutation occurs in any cell, it will most likely to change the gene product ( protein) that is formed by the expression of gene.
In the given question, a mutation has occurred in a heart cell of a developing squirrel. When DNA undergoes transcription and translation, there will be an alteration in the protein product, which will ultimately affect some function in the heart.
Thus, heart will not function properly.