The structure and function remains the same, but exercise enables the heart to pump more blood with each beat, which lowers your heart rate which is good for your long term health
The heart has to pump oxygenn aroound the body faster because when you excercise your body is using up oxygen quicker than normal. The pumps get harder and faster.
The heart starts out as a tube around 5 weeks and then forms 4 chambers. By 24 weeks, the fetus's heart is fully formed. However, the oxygen is supplied through the placenta from the mother's lungs....