The normal heart rate of a woman is about 73 to 77 beats per minute (bpm). It increases to 86 to 90 bpm as the pregnancy progresses.
Heart rate changes begin in the first trimester.
During the first trimester, the heart rate increases to 80-84 bpm.
By the beginning of the second trimester, the heart is pumping 30 % to 50 % more blood than normal.
The smooth muscle relaxes and the arteries dilate to handle the increase in circulating blood volume while maintaining normal blood pressure.
However, the heart rate increases to 82-86 bpm.
By the end of the third trimester, the heart is pumping from 40 % to 90 % more blood than before pregnancy.
The resting heart rate increases to 86-90 bpm.
The chart below shows the average changes in heart rate during pregnancy.