Causes

Exercise has many good effects on the body. For a small number of people, though, it can cause harm. This is because during exercise higher levels of adrenaline and stress affect your body. Your heart requires more oxygen to function. Also, there may be dehydration and electrolyte problems. If you have a normal heart, you can adjust to these changes. But physical activity can sometimes trigger an abnormal heart rhythm if you have certain types of heart disease.

Exercise may be risky for people who are born with certain heart conditions. In people younger than 35 years old, a genetic heart disease is a common cause of SCA. In these cases, people are born with a mutation in a gene that increases the chances of SCA. Some of these include:

• heart muscle disorders, such as hypertrophic cardiomyopathy or arrhythmogenic right ventricular cardiomyopathy
• heart rhythm disorders, such as Wolff-Parkinson-White syndrome, Long QT syndrome, or catecholaminergic polymorphic ventricular tachycardia

Other conditions that increase your risk of SCA:

• being born with an abnormal heart artery
• heart infections
• Marfan syndrome, when the aorta — the main artery of the heart — ruptures

These conditions affect either the electrical or mechanical structure of the heart and may go undetected until sudden cardiac arrest happens. Electrical problems can stop the heart's contractions. Mechanical problems can prevent blood from leaving the heart so not enough flows to the body and this may lead to an electrical problem. Both kinds of problems may give warning signs such as a racing heart, shortness of breath, chest pain or fainting with exercise.

In athletes older than 35, coronary artery disease is the most common heart condition to be a cause of SCA. But even in people with coronary artery disease, exercise can be safe.

For people with coronary artery disease, there are important benefits to exercise. Physical training lowers blood pressure and helps control diabetes and cholesterol.

Also, taking part in cardiac rehabilitation, an exercise-based program, after a heart attack lowers the chances of another heart attack. During exercise, if you feel chest pain, shortness of breath or dizziness, be sure to contact your physician.

Exercise is a good thing, but it's important to talk to your doctor before starting an exercise regimen if you have heart disease.