Pace decreasing, getting tired easily, or chest tightness during running may not simply be fatigue or just a bad day. It could be a warning sign of coronary artery disease or early-stage heart failure, which may only show symptoms during intense physical exertion. Runners, especially those aged 40 and above, should watch for certain symptoms such as palpitations or tightness in the center of the chest radiating to the arm, and undergo an exercise stress test before it progresses to a life-threatening condition.

 

When Fatigue is Not Just Fatigue

There’s a moment many runners remember well: same route, same weather — but by the third, fourth, or fifth step, everything feels unusually heavy. A pace that once felt easy now feels like a full sprint. Breathing becomes difficult, and there’s a fleeting tightness in the center of the chest that comes and goes.
 
Most runners tell themselves, “My form was just bad today,” “I didn’t get enough rest,” or “It’s too hot” and keep running. But sometimes, your body isn’t telling you that you just need rest, it’s also telling you that you need a doctor.
 
News of runners collapsing from cardiac arrest often shocks people, but is forgotten about very quickly. What many don’t realize is that the body almost always sends warning signs in advance — we’re just not trained to recognize them.

Why Running Reveals Hidden Heart Problems

Running is one of the best exercises for the heart, but at the same time, it is also one of the most intense activities for the cardiovascular system.
 
When we run, the heart must pump 4–7 times more blood than when at rest — blood vessels dilate, and the heart muscle must work continuously without pause. If there is any hidden issue or abnormality, running will bring it to light.
 
That’s why symptoms that occur only during running or intense physical exertion should never be ignored. It often means your heart works well enough in daily life but is not strong enough for exercise, and that is a bad sign.
 

3 Warning Signs Runners Should Not Ignore

Running strengthens the heart but, in some cases, subtle abnormalities during exercise may be warning signs of heart disease, especially if they are recurring.
 

1. Unusual drop in pace (more fatigue despite being at the same level of fitness)

If you used to be able to maintain a consistent pace but suddenly:

• Run noticeably slower
• Take longer to complete the same distance
• Feel more fatigued despite the same level of fitness

This may indicate reduced cardiac efficiency or cardiovascular abnormalities.
Many runners assume it is just a bad day, but if it happens repeatedly, a doctor’s visit is recommended. Medically, this may be linked to early heart failure, coronary artery disease, or anemia, all of which reduce oxygen delivery to the muscles.
 

2. Chest tightness during exercise

Chest discomfort, pressure, or tightness is a key symptom of coronary artery disease.
Typical features include:

• Tightness or pressure in the chest
• A squeezing or heavy sensation
• Pain radiating down the arm and/or to the neck or jaw
• Often occurs during physical exertion

If symptoms recur, do not ignore them.
 

3. Palpitations or irregular heartbeat (arrhythmia)

Palpitations during or after exercise may indicate abnormalities in the heart’s electrical system.
Warning signs include:

• Unusually fast or stronger heartbeat
• Skipped or irregular beats
• Dizziness or near-fainting

Running can alter electrolyte balance, stimulate the autonomic nervous system, and increase adrenaline — conditions that can trigger an arrhythmia that may be hidden. Some runners only discover this after noticing abnormal readings on a heart rate monitor.
 

Warning signs: When to stop and seek help immediately

• Severe chest pain radiating down the left arm and/or to the neck or jaw
• Shortness of breath, cold sweating, pale skin
• Feeling faint or losing consciousness
• Chest pain that does not resolve within 5 minutes after stopping

 

Risk Factors Runners Should Know

Having risk factors doesn’t mean you shouldn’t run; it just means that you have to run smarter.
 

Unmodifiable risk factors	Modifiable risk factor
Age: Over 40 for men; over 50 for women	Untreated high blood pressure
A history of family members developing heart disease before age 55	High cholesterol (high LDL/low HDL)
Being male (higher risk in middle age)	Diabetes or pre-diabetes
Congenital heart disease (even if treated)	Smoking, including having quit within the past 2 years
History of severe COVID-19 or myocarditis	Chronic stress and lack of sleep

 
Being extremely fit does not mean you are risk-free. Well-trained runners often have a higher pain tolerance, making them more likely to ignore the warning signs.
 

Who Should Undergo a Heart Check-up?

You should consider getting a heart check-up if:

• Your running performance has dropped abnormally
• You experience chest tightness during exercise
• You have palpitations or an irregular heartbeat
• Symptoms recur
• Running feels different than before

 
A heart check-up is not about restricting you from running; it’s about ensuring that running is safe for you.
 

Heart-Safe Running

• Train using heart rate (HR) zones; Zone 2 (60–70% max HR) is best for long-term heart health
• Track your pace consistently; abnormal changes are easier to detect with a monitor
• Take warming-up and cooling-down seriously; sudden HR changes put you at high-risk for a heart issue
• Get a heart check-up every 1–2 years, especially if you are over 40 or have risk factors
• Rest when your body requires it; overtraining increases your risk of arrhythmia
• Stay hydrated; dehydration increases your cardiac workload and risk of arrhythmia

 
   

Frequently Asked Questions (FAQ)

 
Q: If I feel unusually fatigued while running, should I get my heart checked?
A: It depends on the frequency and accompanying symptoms, such as chest tightness, palpitations, and dizziness. If these symptoms occur repeatedly, see a doctor as soon as possible. If they are one-time events after poor rest or an illness, it may not be serious; however, regular runners should still have periodic heart check-ups.
 
Q: Is chest tightness during running dangerous? How is it different from exercise-related transient abdominal pain (ETAP)?
A: ETAP usually occurs on one side of the abdomen and improves with a slower pace or deep breathing. Cardiac chest pain feels like there is pressure in the center of your chest, which may radiate to the left shoulder or neck, and does not improve with breathing changes. If you’re unsure, stop and take the necessary precautions.
 
Q: Should marathon runners get a heart check-up before racing?
A: Yes. A heart check is highly recommended — especially for those over 40 or those with risk factors. An exercise stress test can help assess how well your heart handles endurance-level exertion.
 
Q: My smartwatch is showing an abnormal heart rate. What should I do?
A: Optical sensors may be inaccurate during fast movement. However, if abnormal readings occur frequently along with symptoms, record the data and consult a doctor. Chest strap monitors provide better accuracy.
 
Q: If a heart check-up discovers abnormalities, can I still run?
A: It depends on the condition and severity. Many people can continue running with an adjusted intensity and proper management. The goal of a screening is not to stop you from running; it’s to make running sustainably.
 

By Dr. Tanaporn Laprattanagul, Cardiac Rehabilitation Specialist at the Physical Medicine and Rehabilitation Center