The image of a "heart of a woman" in Portia's speech highlights her emotional vulnerability and strength, particularly in relation to her love and concern for Brutus.
Therefore, the most accurate impact on the audience would be:
It shows the audience that Portia loves her husband and is worried about him.
This line reflects her deep affection for Brutus and her anxiety about his involvement in the conspiracy against Caesar, emphasizing her emotional turmoil and the gender expectations of the time. Instead of suggesting jealousy or deceit, it illustrates her genuine feelings of concern and helplessness in the face of the dangerous events unfolding.