An electrocardiogram (EKG or ECG) measures the heart’s electrical activity. This allows doctors to check for irregularities that may signal heart disease. Some evidence suggests that EKGs can predict future heart attack risk.

An EKG is usually a quick test, measuring a few seconds to a few minutes of heart activity. The heart has a complex electrical system. Errors and irregularities in this electrical system often mean an issue with the heart, such as a blockage or damage to one of the heart’s chambers.

These issues may increase the risk of heart attack and other types of heart disease. An EKG reading may also help diagnose a heart attack. However, no screening test is perfect, and an EKG cannot completely rule out the potential to have a heart attack. Its role is primarily as a risk assessment tool.

Read on to learn more about EKG and whether it can predict a person’s risk of future heart attacks.

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An EKG measures the electrical activity in the heart. It shows several different patterns. The upper chambers of the heart make a P wave when they contract. Next, the bottom chambers of the heart contract in a QRS complex. The last wave — a T wave — is the moment when the heart rests.

Measuring the time an electrical signal takes to pass from one area of the heart to another can help doctors diagnose heart health issues such as blockages and electrical irregularities, including heart arrhythmias.

An EKG can also rule out certain heart conditions when an individual has symptoms such as:

Research from 2019 found that EKG results were a more effective risk prediction tool than traditional methods of assessing heart attack risk. Still, people usually need additional testing for doctors to conclusively diagnose a heart condition.

A stress test may also be beneficial. This involves a person walking on a treadmill while connected to an EKG machine. A doctor can monitor the individual and their EKG to look for signs of ischemia or blood flow issues to the heart. This test is an example of how EKG can predict heart attack risk directly.

Learn how to recognize the signs of a heart attack and what to do.

Not all heart attacks cause severe symptoms. Some even resolve on their own without treatment. However, these silent heart attacks still cause damage by depriving areas of the heart of oxygen. These regions eventually scar over.

The damage can cause changes on an EKG for years. Specifically, the damaged areas may affect the electrical signals in the heart, changing the results of an EKG. For example, when a person shows no current signs of a heart attack but irregular Q waves appear on EKG, it may signal a prior heart attack.

Doctors have historically looked at an individual’s medical history and the results of various tests to determine a person’s heart attack risk. This includes results from tests assessing the following:

However, emerging research suggests that an EKG might be just as effective.

In a 2019 study, researchers assigned participants a heart attack risk score based on their history or an EKG reading. The EKG was an effective predictor of heart attack risk and often outperformed traditional measures.

EKG and other heart conditions

People with the following may have a higher heart attack risk:

An EKG can detect these irregularities.

Several tests can predict a person’s risk of a future heart attack, especially over the next few years:

  • Blood tests: These can measure cholesterol and triglyceride levels. High readings increase the risk of heart disease. Bloodwork can also measure blood sugar, which is an important predictor of diabetes, as well as a measure of how well-managed existing diabetes is.
  • Body measurements: Tests that show very high body fat — including a large waist circumference — can show heart attack risk.
  • Blood pressure: High blood pressure is a heart disease risk factor.

Drawing upon data from a person’s history and test scores, such as cholesterol measurement, a doctor may assign an individual a 10-year risk score to assess their heart attack risk relative to others.

An EKG can only measure electrical activity for the time it is attached. This is often a very short period, usually a few seconds to a few minutes. If a person has infrequent heart issues, such as atrial fibrillation that only occurs every few days, an EKG might not detect it.

For this reason, doctors may recommend ongoing monitoring of people with heart health symptoms. One option is a Holter monitor. This is a type of EKG an individual wears for an extended period — usually a day or longer.

Learn more about 24-hour Holter monitoring.

Here are some answers to common questions on EKG and heart health.

Will an EKG show a blockage?

An EKG can show ischemia. This typically occurs due to a blockage in an artery of the heart, reducing blood flow to the organ. This lack of blood flow can cause changes that appear on EKG. Still, the exact location of the blockage cannot be known without doctors performing a procedure called left heart catheterization.

Stress tests help determine whether someone has ischemia. A person should expect to walk on a treadmill while attached to the EKG machine to monitor heart activity.

Does a good EKG mean a healthy heart?

An EKG can only rule out some heart conditions but cannot detect all heart issues. For example, a person with periodic heart rate irregularities may get a typical EKG result if the irregular heart rate is not present at the test time.

EKGs are not the only diagnostic tool doctors use to assess heart health.

Learn about how to help improve heart health.

What are the 4 silent signs of a heart attack?

Silent heart attacks cause mild symptoms that a person may ignore. Most people, though, still have symptoms.

Symptoms can vary between individuals. Older people, especially females or those with diabetes, often have nonspecific symptoms such as heartburn or nausea.

Signs to look for include:

  • chest pain, even if it is mild
  • unexplained pain in other areas of the body, such as stomach or jaw pain
  • shortness of breath or dizziness
  • nausea and cold sweats

An EKG measures electrical activity in the heart. Irregularities in this electrical activity may provide evidence of a past heart attack or point to heart health issues that predict future heart attacks.

EKGs can predict a person’s risk of a heart attack — it cannot calculate anyone’s exact risk nor completely rule out the potential for a heart attack. Alongside other data, including an individual’s medical and family history, an EKG may help assess overall heart health and heart disease risk.