A faster heartbeat during pregnancy is one of the most common cardiovascular changes your body makes, and in most cases it’s completely normal. Your heart rate rises progressively throughout pregnancy, reaching an average of about 91 beats per minute (with a normal range of 68 to 115) by around 34 weeks. That increase is driven by a massive expansion in blood volume and the extra demands of supporting a growing baby. That said, some causes of a racing heart during pregnancy deserve attention.
Why Your Heart Works Harder During Pregnancy
Your body undergoes a dramatic cardiovascular overhaul starting in the first trimester. By eight weeks of pregnancy, your heart is already pumping about 20% more blood per minute than it did before conception. That number climbs to roughly 40% above your pre-pregnancy baseline, peaking somewhere between 20 and 28 weeks.
The reason is simple: you have a lot more blood to move. Total blood volume increases by about 45%, adding 1,200 to 1,600 milliliters of extra fluid to your circulation. Plasma volume alone rises by more than 50 to 60% by late in the third trimester. Your heart compensates by beating faster and pumping more blood with each beat, which is why you notice your pulse running higher than usual even when you’re sitting still.
Hormones and Your Heart Rate
Progesterone, which surges throughout pregnancy, plays a direct role in speeding up your heart. Rising progesterone levels coincide with the increase in heart rate and the amount of blood your heart pumps per beat. This hormone also affects the electrical activity of heart muscle cells, altering how quickly they fire and recover. Estrogen contributes too, relaxing blood vessel walls and lowering your blood pressure, which in turn triggers your heart to beat faster to maintain adequate circulation.
Iron Deficiency and Anemia
If your heart feels like it’s racing more than you’d expect, anemia could be a factor. Iron deficiency is extremely common in pregnancy because your body needs to produce all that extra blood, and iron is essential for making the red blood cells that carry oxygen. When iron stores run low, your body has fewer oxygen-carrying cells to work with. The heart compensates by pumping faster to deliver the same amount of oxygen to your tissues.
In one study of pregnant women with iron deficiency anemia in the second trimester, 90% had a rapid heart rate and abnormal electrical heart readings. The lower the hemoglobin and iron storage levels dropped, the faster the heart rate climbed. This is one of the most treatable causes of a fast heartbeat in pregnancy, so it’s worth mentioning to your provider if you’re also feeling unusually tired, dizzy, or short of breath.
How Your Position Affects Your Pulse
Lying flat on your back, especially in later pregnancy, can trigger a noticeable jump in heart rate. The growing uterus compresses a large vein called the inferior vena cava, which carries blood back to your heart from your lower body. When that vein is squeezed, less blood returns to the heart, blood pressure drops, and your heart speeds up to compensate. This is sometimes called supine hypotensive syndrome, defined as a blood pressure drop of 15 to 30 points or a heart rate increase of 20 beats per minute when lying on your back.
The fix is straightforward: roll onto your left side. Studies show a significant decrease in heart rate when pregnant women shift from lying on their back to lying in a left lateral position. This keeps the uterus off the vein and restores normal blood flow.
Thyroid Changes During Pregnancy
Pregnancy naturally pushes thyroid hormone levels higher. Two hormones that rise during pregnancy, hCG and estrogen, both increase measured thyroid hormone levels in the blood, which makes thyroid problems tricky to diagnose. But genuine hyperthyroidism (an overactive thyroid) speeds up many body functions, including your heart rate. If your racing heart comes with unexpected weight loss, trembling hands, heat intolerance, or trouble sleeping, your provider can run a simple blood test to check thyroid function.
Everyday Triggers Worth Watching
Beyond the big physiological shifts, a few everyday factors can push your already-elevated heart rate even higher:
- Caffeine: Stick to one cup of coffee a day, and go easy on chocolate and other caffeinated foods. Caffeine stimulates your nervous system and can make palpitations more noticeable.
- Dehydration: Your body needs significantly more fluid during pregnancy. When you’re even mildly dehydrated, blood volume drops, and your heart speeds up to compensate. Keeping a water bottle close and sipping throughout the day helps.
- Anxiety and stress: Pregnancy itself can be a source of stress, and the adrenaline response that comes with worry directly increases heart rate. Deep breathing and rest can help break the cycle.
What to Do if Your Heart Races Suddenly
If you feel a sudden episode of a pounding or racing heart while otherwise feeling stable, vagal maneuvers are the recommended first step. These are simple physical techniques that stimulate a nerve responsible for slowing your heart rate. They include bearing down as if you’re having a bowel movement (a Valsalva maneuver) or briefly immersing your face in cold water. Research reviews confirm these techniques are well tolerated in all three trimesters of pregnancy and are considered the safest initial response to a sudden rapid heartbeat.
When a Fast Heart Rate Needs Attention
There is no single cutoff that separates “normal pregnancy heart rate” from “too fast.” A threshold of 100 beats per minute catches too many healthy pregnant women, while 120 beats per minute risks missing real problems. The truth falls somewhere between, and it depends partly on what your pre-pregnancy resting rate was.
What matters more than a specific number is the pattern and the symptoms that come with it. A persistently elevated heart rate that doesn’t come down with rest, position changes, or hydration is worth investigating. The same goes for episodes accompanied by chest pain, fainting, severe shortness of breath at rest, or feeling like your heart is beating irregularly rather than just fast. These symptoms can occasionally point to conditions like an abnormal heart rhythm or a structural heart issue that needs treatment during pregnancy, and basic testing can usually sort it out quickly.