Feeling your own heartbeat is usually normal. Your body has pressure sensors called baroreceptors in your blood vessels that detect each beat and relay that information to your brain. Most of the time, your brain filters out this signal so you don’t notice it. But certain conditions, body positions, emotions, and substances can amplify the sensation enough that it breaks through into conscious awareness. Doctors call this sensation “palpitations,” and it accounts for 16% of all visits to primary care physicians, making it one of the most common reasons people seek medical attention.
Why Your Brain Usually Blocks It Out
Your heart beats roughly 100,000 times a day, and you’re unaware of the vast majority of them. That’s by design. Baroreceptors in your arteries fire with every heartbeat, sending timing and force data to your brain. Your brain uses this information to predict when the next beat will arrive and actively dampens the signal so it doesn’t compete with what you’re seeing, hearing, or touching. Researchers describe this as a constant shift between internal body awareness and external awareness. When your brain’s filtering system is working normally, external sensations win out, and your heartbeat stays in the background.
When something disrupts that balance, the heartbeat signal gets louder. A stronger-than-usual beat, a faster heart rate, a quiet room with no competing sensory input, or heightened attention to your body (like during anxiety) can all tip the scales toward internal awareness. That’s the moment you suddenly “feel” your heart.
Common Harmless Triggers
Most episodes of feeling your heartbeat trace back to everyday causes that are temporary and not dangerous:
- Caffeine and stimulants. Caffeine increases heart rate and the force of each contraction, making individual beats easier to detect. Energy drinks, pre-workout supplements, and some medications have similar effects.
- Stress and strong emotions. Adrenaline makes your heart beat harder and faster. Anxiety is particularly effective at creating palpitations because it also shifts your attention inward, so you’re more likely to notice what your heart is doing.
- Dehydration. When blood volume drops, your heart compensates by beating faster to maintain circulation. Even mild dehydration from skipping water on a hot day can produce noticeable palpitations.
- Exercise. During and immediately after physical activity, your heart rate and stroke force increase. Feeling your heart pound after a run is completely expected.
- Pregnancy. Blood volume increases significantly during pregnancy, and the heart works harder to pump it. Many pregnant people notice their heartbeat for the first time during the second or third trimester.
- Certain medications. Decongestants, asthma inhalers, and some antidepressants can raise heart rate or increase cardiac output enough to produce awareness of the heartbeat.
Why It’s Louder When You Lie on Your Left Side
If you’ve noticed your heartbeat feels strongest when you roll onto your left side in bed, there’s a straightforward anatomical explanation. Your heart sits behind your sternum, mostly centered in your chest, but its lower tip (the apex) angles slightly to the left. The apex is primarily made up of the left ventricle, which is the chamber responsible for pumping blood out to the rest of your body. It generates the most force of any chamber.
When you lie on your left side, gravity shifts the apex closer to your chest wall. At the same time, the weight of your body against the mattress slightly compresses your rib cage, closing the remaining gap. The result is that the strongest pumping action of your heart lands almost directly against the inside of your chest wall, producing a noticeable thump that can feel surprisingly intense. Rolling onto your back or right side usually resolves it immediately.
Heart Rhythm Issues That Cause Palpitations
Sometimes what you’re feeling isn’t just a normal heartbeat that broke through your awareness. It’s a heartbeat that genuinely isn’t behaving normally. Several types of rhythm disturbances produce distinct sensations.
Premature or extra heartbeats are the most common. The electrical signal telling the heart to beat arrives too early, creating a brief pause followed by a stronger-than-normal contraction when the rhythm resets. This often feels like a skipped beat, a flutter, or a sudden thud. Nearly everyone experiences premature beats occasionally, and isolated ones are almost always harmless.
Atrial fibrillation is the most common sustained arrhythmia, affecting more than 2.5 million people in the United States. In this condition, the upper chambers of the heart fire chaotically rather than in a coordinated rhythm, and the upper and lower chambers fall out of sync. People with atrial fibrillation often describe a quivering, racing, or irregular sensation in their chest that may come and go or persist for hours.
Supraventricular tachycardia (SVT) causes episodes of very rapid heartbeat that start and stop abruptly. People often describe it as a sudden switch flipping on, with the heart racing at 150 to 250 beats per minute, and then stopping just as suddenly. Episodes can last seconds or hours.
Medical Conditions Beyond the Heart
Not every palpitation originates from a heart problem. An overactive thyroid gland is one of the most well-established non-cardiac causes. Excess thyroid hormone decreases resistance in blood vessels while simultaneously increasing heart rate, the force of each contraction, and total blood volume. The combined effect can push cardiac output 50% to 300% higher than normal. People with hyperthyroidism frequently report palpitations along with exercise intolerance, shortness of breath, and sometimes develop atrial fibrillation as a direct result of the hormone excess.
Anemia, where the blood carries fewer oxygen-delivering red blood cells than it should, forces the heart to beat faster to compensate. The result is a racing or pounding sensation, especially during physical activity. Iron deficiency is the most common cause, but thyroid problems themselves can contribute: hypothyroidism (the opposite of an overactive thyroid) is associated with anemia in up to 35% of cases, creating a less obvious but still significant source of palpitations.
How Doctors Figure Out the Cause
The tricky thing about palpitations is that they often aren’t happening when you walk into the doctor’s office. Diagnosis typically starts with an electrocardiogram (ECG), a painless test where electrodes on your chest record your heart’s electrical activity in real time. If your heart happens to be misbehaving during the test, the ECG will catch it. But many arrhythmias are intermittent, so a normal ECG doesn’t rule everything out.
For palpitations that come and go, your doctor may have you wear a Holter monitor, a portable ECG device that records continuously for 24 hours or longer while you go about your daily routine. If your episodes are even less frequent, an event recorder works differently: you wear it for up to 30 days and press a button when you feel symptoms, capturing the heart’s rhythm at that exact moment. Some smartwatches now offer similar remote ECG monitoring that can catch irregular rhythms between doctor visits.
If a structural problem is suspected, an echocardiogram uses ultrasound to create a moving picture of the heart, showing how the valves and chambers are functioning. Blood tests to check thyroid levels and red blood cell counts help identify systemic causes that may be driving the palpitations from outside the heart itself.
What Treatment Looks Like
For palpitations caused by lifestyle factors, the fix is often straightforward: cut back on caffeine, drink more water, manage stress, or adjust a medication that’s contributing. Many people find that once they identify their trigger, the episodes become predictable and manageable.
When an arrhythmia is the cause, treatment depends on the type and severity. For persistent fast heart rates, doctors commonly prescribe beta-blockers, medications that block the effects of adrenaline on the heart. They slow the heart rate and reduce the force of contractions, making individual beats less noticeable and preventing certain arrhythmias from taking hold. For conditions like atrial fibrillation or SVT, additional interventions may be needed to restore a normal rhythm or prevent complications like blood clots.
If a thyroid disorder or anemia is driving the palpitations, treating the underlying condition typically resolves the cardiac symptoms. Thyroid levels can be normalized with medication, and anemia often improves with iron supplementation or addressing whatever is causing the deficiency.
Signs That Need Immediate Attention
Most palpitations are harmless, but certain accompanying symptoms signal a potentially serious problem. Seek emergency care if you feel your heartbeat along with chest pain or discomfort, fainting or loss of consciousness, severe dizziness, or severe shortness of breath. These combinations can indicate that the heart isn’t pumping blood effectively, which requires urgent evaluation. Palpitations that occur during exertion, last for extended periods, or progressively worsen over days also warrant prompt medical assessment rather than a wait-and-see approach.