Shot To The Heart

It was a joke that I saw on the internet:

Aging Mildred was a 93 year-old woman who was particularly despondent over the recent death of her husband Earl. She decided that she would just kill herself and join him in death.

Thinking that it would be best to get it over with quickly, she took out Earl's old Army pistol and made the decision to shoot herself in the heart since it was so badly broken in the first place.

Not wanting to miss the vital organ and become a vegetable and burden to someone, she called her doctor to inquire as to just exactly where the heart would be.

"On a woman," the doctor said, "your heart would be just below your left breast." Later that night, Mildred was admitted to the hospital with a gunshot wound to her knee.

I know that the woman didn't know where the heart is, but I don't know the ha ha point of this joke. Does anyone know it?