So, you woke up, checked your Apple Watch or Garmin, and saw the number 43 staring back at you. Your first instinct might be to panic. Most of us grew up hearing that a "normal" pulse is somewhere between 60 and 100 beats per minute. Seeing a resting heart rate 43 feels like you're bordering on hibernation territory.
But here is the thing.
Context is everything in cardiology. If you are an endurance athlete who spends twelve hours a week on a bike, 43 might be your badge of honor. If you’re a sedentary office worker who feels dizzy every time you stand up, that same 43 is a flashing red light. We call this bradycardia—the medical term for a heart rate below 60—but whether it’s "athletic bradycardia" or a sign of "sick sinus syndrome" depends entirely on how your body is actually functioning.
The Science of the Slow Pulse
Your heart is a pump. It’s a muscle, plain and simple. Like any other muscle, it gets stronger with use. When you perform high-volume aerobic exercise, your heart’s left ventricle actually undergoes structural changes. It gets bigger. It gets more efficient. It can push out more blood with a single squeeze. This is what doctors call an increased stroke volume.
Because each beat is so powerful, the heart doesn't need to cycle as often to keep your oxygen levels steady. That's why elite cyclists like Miguel Induráin reportedly had a resting heart rate in the high 20s. For them, a resting heart rate 43 would actually be an "off" day or a sign of overtraining.
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However, if you aren't training for a marathon, a heart rate this low can mean the electrical system in your chest is misfiring. The sinoatrial (SA) node—your body's natural pacemaker—might be sluggish. Or perhaps the electrical signal is getting blocked as it travels from the top chambers (atria) to the bottom chambers (ventricles).
When Resting Heart Rate 43 is a Problem
It’s not just about the number. It’s about the symptoms. Doctors generally don't treat a number; they treat a patient. If you have a resting heart rate 43 and you feel fantastic, most cardiologists will tell you to keep doing what you’re doing. But there are specific "red flag" symptoms that change the conversation immediately.
- Syncope (Fainting): If you’re actually losing consciousness, your brain isn't getting enough blood. This is the most serious sign.
- Near-syncope: That "gray out" feeling where the world goes fuzzy when you stand up.
- Exercise Intolerance: You used to run three miles easily, but now you’re winded walking to the mailbox. This suggests your heart can't "rev up" its rate when the body demands more oxygen.
- Chest Pain: Sometimes a slow rate is tied to underlying coronary artery disease.
- Mental Confusion: "Brain fog" can sometimes be traced back to low cardiac output.
Honest talk? If you’re over 65 and your heart rate has naturally drifted down to 43 without a history of intense athletics, it’s worth a conversation with a professional. Aging can cause "wear and tear" on the electrical pathways, leading to a condition called heart block. It's common, and honestly, it's often the reason people end up getting pacemakers.
The Role of Medication and Diet
Sometimes we do this to ourselves. Beta-blockers (like Metoprolol or Atenolol) are designed to slow the heart rate to reduce blood pressure or manage anxiety. If your dosage is a bit too high, you might find yourself sitting at a resting heart rate 43 and feeling like a zombie. Calcium channel blockers can do the same thing.
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Even your supplements matter. High doses of magnesium or certain herbal remedies can impact your rhythm. Electrolyte imbalances—specifically potassium levels that are too high (hyperkalemia) or too low—can mess with the electrical conductivity of your heart cells. If you’ve been doing a hardcore keto diet or using "light salt" (which is pure potassium) excessively, your heart rhythm might pay the price.
Then there’s the thyroid. Hypothyroidism (an underactive thyroid) acts like a brake pedal for your entire metabolism. Your temperature drops, your digestion slows down, and your heart rate sinks. I've seen cases where treating the thyroid brought a "scary" low heart rate back into the 50s within weeks.
How to Properly Measure It
Don't trust a single reading from a wrist-worn wearable. Those sensors use photoplethysmography (PPG)—basically using light to track blood flow—and they can be notoriously finicky. If your watch band is loose, or if you have dark tattoos on your wrist, the reading might be off.
The gold standard for a DIY check is the manual carotid pulse. Two fingers on the neck, count for 60 seconds. Do this right when you wake up, before you’ve had coffee or checked your emails. If the manual count confirms a resting heart rate 43, then it’s time to look at the data trends over a week. One night of deep sleep after a glass of wine might tank your HR temporarily, but a consistent 43 is a physiological statement.
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The "Athlete's Paradox"
There is a fascinating, slightly scary phenomenon called the "athlete's paradox." While a low heart rate is usually a sign of fitness, some studies—specifically those published in journals like Heart—suggest that decades of extreme endurance training might increase the risk of atrial fibrillation (Afib) later in life.
Basically, you can stretch the heart so much that it develops tiny bits of scar tissue. This doesn't mean you shouldn't exercise. It just means that even if you're "fit," you aren't invincible. A resting heart rate 43 in a 50-year-old triathlete is usually fine, but if that pulse feels "floppy" or irregular, it's a different story than a steady, rhythmic 43.
Actionable Steps for Management
If you’ve discovered your heart is ticking at 43 beats per minute, don't just sit there googling yourself into a panic attack. Follow a logical progression of self-assessment.
- Audit your symptoms. Keep a "symptom diary" for three days. Note if you feel dizzy, tired, or short of breath during daily tasks. If you feel 100% fine, your 43 is likely just your unique baseline.
- Check your meds. Look at every bottle in your cabinet. If you see anything ending in "-olol," that's a beta-blocker. If you're on these and feeling lethargic, call your prescribing doctor to discuss a dosage tweak.
- Hydrate and balance. Ensure you're getting enough sodium, potassium, and magnesium through whole foods. Dehydration can sometimes cause "paradoxical bradycardia" in certain individuals, though it usually causes a fast heart rate.
- Get an EKG. If the number 43 is new or accompanied by any weird feelings, a simple 10-second EKG at a clinic can tell a doctor if you’re in a healthy "Sinus Bradycardia" or a more complex "Heart Block."
- Sleep Study. Sometimes, a low heart rate at night is linked to Sleep Apnea. If you snore or wake up feeling unrefreshed, the 43 might be your heart’s reaction to drops in oxygen levels during the night.
Living with a resting heart rate 43 is often just a quirk of being a healthy, active human. It’s a sign of an efficient engine. But the moment that efficiency turns into insufficiency—where you can't power your brain or your muscles because the pump is too slow—that's when you move from "fit" to "finding a cardiologist." Listen to your body, not just your watch.