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A Sudden Drop in Heart Rate During Exercise

Heart rate refers to the number of times your heart beats per minute. When at rest, a healthy adult heart beats about 60 to 100 times, and some athletes' hearts beat about 40 times per minute. During exercise, when your body requires more oxygen, the heart beats faster to distribute oxygen-rich blood, and your heart rate can increase threefold, but should not drop. The causes of a sudden drop in heart rate range from a malfunctioning heart rate monitor to heart disease.

Slow Heart Rate

The medical term for an abnormally slow heart rate is bradycardia. Bradycardia refers to a heart rate of fewer than 60 beats per minute, and is described by as a disruption to the electrical impulses controlling your heart rate. While it’s not always a serious problem, if your heart is not pumping oxygen-rich blood to the body, it can cause dizziness, weakness, shortness of breath, chest pains, confusion, fatigue and fainting. A variety of conditions can cause your heart rate to suddenly plummet, including age-related heart tissue degeneration, heart disease, high blood pressure, a congenital heart defect, heart infection, hypothyroidism, electrolyte imbalance, sleep apnea and medications.

Other Causes

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If the spike in blood pressure is not caused by the typical suspects, your doctor may consider complications like a severe infection, an allergic reaction or even a malfunctioning heart rate monitor. If you’re using the heart rate monitor on gym equipment, be sure the sensors are clean before using them. Also, understand that monitors on gym equipment can malfunction, especially if the equipment is old. Sometimes the equipment’s electronics need to be rebooted. If you’re using a wireless monitor, the lines from your machine can get crossed with another machine.


No doctor can diagnose the cause of your heart rate problem without conducting a battery of tests, as well as getting your medical history, including your family's medical history. You may be asked to complete a stress test by walking on a treadmill or riding a stationary exercise bike while your heart rate and blood pressure are monitored. When you reach your target heart rate, the monitoring device may show that your heart is becoming oxygen deprived, or you may experience complications such as chest pain or a sudden rise or drop in blood pressure.


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Take action to prevent the onset of age-related heart problems. Continue exercising regularly, and if you smoke, quit. Also, make sure to stay hydrated during exercise, as dehydration can cause your heart rate to plummet.