A resting heart rate above 100 beats per minute is considered high, a condition called tachycardia. For most adults, the normal resting range is 60 to 100 bpm. If your pulse is consistently landing above that upper limit, or even creeping toward it in ways that feel new, something is pushing your heart to work harder than it should at rest.
The causes range from completely harmless (you just had coffee) to worth investigating (thyroid problems, anemia, anxiety disorders). Here’s how to sort through what might be going on.
How to Get an Accurate Reading First
Before worrying about a high number, make sure you’re measuring correctly. The best time to check your resting heart rate is first thing in the morning, before you get out of bed. Place your index and middle fingers on the inside of your wrist just below the thumb, or on the side of your neck next to the windpipe. Count the beats for 15 seconds and multiply by four.
If you checked your pulse after climbing stairs, drinking coffee, or having a stressful phone call, that number doesn’t reflect your true resting rate. Recheck after sitting quietly for at least five minutes, ideally in the morning over several days, to see if the pattern holds.
Caffeine, Stimulants, and Decongestants
Caffeine is one of the most common reasons for a temporarily elevated pulse. It blocks the breakdown of a signaling molecule in your cells that makes heartbeats more forceful, and it triggers the release of adrenaline. The combination can noticeably speed up your heart rate, especially if you’re sensitive to it or had more than usual.
Other stimulants do the same thing through similar pathways. Energy drinks, certain ADHD medications, nicotine, and even over-the-counter cold medicines containing decongestants like pseudoephedrine can all push your heart rate up. Inhaled bronchodilators used for asthma (like albuterol) are another well-documented cause. If your pulse climbed after starting a new medication or supplement, that’s a strong clue.
Dehydration
When you’re low on fluids, your blood volume drops. Your heart compensates by beating faster to maintain the same circulation. This is one of the simplest and most overlooked explanations, especially if you’ve been exercising, sweating heavily, sick with vomiting or diarrhea, or just not drinking enough water throughout the day. Rehydrating often brings the pulse back down within an hour or two.
Stress, Anxiety, and Panic
Your nervous system has a direct line to your heart rate. When you’re stressed or anxious, your body releases adrenaline and other stress hormones that speed up your pulse as part of the fight-or-flight response. This can happen even when you don’t feel particularly anxious on a conscious level. Chronic stress keeps your baseline heart rate elevated over time.
Panic attacks take this to an extreme. During an acute episode, heart rate can spike to 200 bpm or higher, which is why many people experiencing a panic attack believe they’re having a heart attack. The rapid heartbeat usually subsides within 20 to 30 minutes as the panic passes. If you’re noticing frequent episodes of sudden, unexplained heart racing paired with chest tightness, shortness of breath, or a sense of dread, anxiety disorders are worth exploring with a doctor.
Fever and Infection
Your heart rate rises predictably with your body temperature. For every 1°C (about 1.8°F) increase in body temperature, your pulse goes up by roughly 7 to 10 beats per minute, with a slightly larger increase in women than men. So if you have a fever of 102°F, your resting heart rate might be 15 to 20 bpm higher than normal just from the fever alone.
This is your body’s way of circulating immune cells faster and delivering more oxygen to tissues fighting the infection. Your pulse should return to normal as your temperature comes down. If it stays elevated well after the fever breaks, that’s worth noting.
Thyroid Problems
An overactive thyroid gland (hyperthyroidism) is one of the most important medical causes to rule out. Your thyroid produces hormones that directly regulate heart rate. When it produces too much, your heart speeds up, sometimes significantly. Along with a fast or pounding heartbeat, hyperthyroidism often causes unintentional weight loss, feeling unusually warm, trembling hands, irritability, and difficulty sleeping.
Left untreated, hyperthyroidism can lead to serious heart complications, including an irregular heart rhythm called atrial fibrillation and, over time, heart failure. A simple blood test can check your thyroid hormone levels, and treatment is straightforward once diagnosed.
Anemia and Low Iron
When your blood doesn’t carry enough oxygen, either because you have fewer red blood cells or less hemoglobin, your heart beats faster to compensate. This is anemia, and it’s especially common in women with heavy periods, people with iron-poor diets, and those with chronic conditions that affect nutrient absorption. You might also feel unusually tired, dizzy, short of breath with minimal exertion, or notice pale skin. A basic blood panel can identify it.
POTS and Position-Related Changes
If your pulse seems fine when you’re lying down but jumps dramatically when you stand up, you may be dealing with a condition called postural orthostatic tachycardia syndrome (POTS). The diagnostic hallmark is a heart rate increase of 30 bpm or more (40 bpm for people under 19) within 10 minutes of standing, without a significant drop in blood pressure. Symptoms typically include lightheadedness, brain fog, and fatigue, and they need to be present for at least six months to meet diagnostic criteria.
POTS is more common in young women and often develops after a viral illness, surgery, or pregnancy. It’s frequently underdiagnosed because the symptoms overlap with anxiety and dehydration.
Sleep Deprivation and Physical Deconditioning
Poor sleep raises your resting heart rate. Even one night of significantly reduced sleep can increase your pulse the next day, and chronic sleep deprivation keeps it elevated. If you’ve been sleeping fewer hours or sleeping poorly, this alone could explain what you’re seeing.
Physical fitness matters too. Well-trained athletes often have resting heart rates in the 40s or 50s because their hearts pump more blood per beat. The opposite is also true: if you’ve been sedentary for weeks or months, your resting rate drifts upward. Gradually increasing your cardiovascular exercise is one of the most effective ways to bring a high resting pulse down over time.
Alcohol and Recreational Drugs
Alcohol is a well-documented trigger for elevated heart rate, particularly in larger amounts. It can cause or worsen irregular heart rhythms even in people without underlying heart conditions. Cocaine and amphetamines flood the body with adrenaline-like chemicals, causing dramatic spikes in heart rate that can be dangerous. If substance use lines up with when you noticed the change, that connection is probably not a coincidence.
Warning Signs That Need Immediate Attention
A temporarily fast pulse after coffee or exercise is not an emergency. But a rapid heart rate paired with certain other symptoms signals something more urgent. Chest pain or pressure, fainting or near-fainting, severe shortness of breath at rest, and confusion alongside a racing pulse all warrant emergency evaluation. The same is true if your resting heart rate is persistently above 100 bpm with no obvious explanation, or if you feel your heart beating irregularly rather than just fast.