For overweight and obese people with a common heart rhythm problem, improving cardiovascular fitness with exercise may help to eliminate symptoms, a recent Australian study found.

Participants with the greatest improvements in their cardio fitness were less burdened by symptoms of the arrhythmia, known as atrial fibrillation, and more likely to survive symptom free during the study, compared to those who had smaller or no fitness improvements.

A possible side effect of the cardio exercise regimen, weight loss, may have also contributed to the improvements, researchers say.

Obesity is a risk factor for heart rhythm problems, said the study’s lead author Prash Sanders, director of the Center for Heart Rhythm Disorders at Royal Adelaide Hospital. And “atrial fibrillation (AF) is a growing epidemic,” he said in an email.

In atrial fibrillation, the heart beats rapidly and irregularly, which can promote the formation of clots and cause problems with blood flow.

The condition, sometimes known as A-Fib or AF, affects more than 33 million people worldwide, Sanders and colleagues write in the Journal of the American College of Cardiology.

While weight loss has been shown to help with heart rhythm issues, the study team wanted to determine how cardio fitness might benefit overweight people struggling with heartbeat irregularities.

At the start of the study and four years later, 308 overweight and obese volunteers with atrial fibrillation complete questionnaires that asked how often they experienced heartbeat irregularities, how long the episodes lasted and how severe they were.

The researchers also had patients wear a heart monitor for seven days at a time.

Based on exercise stress testing at the start of the study, 95 people were classified as having low cardio fitness, 134 had adequate fitness and 79 were classified as high fitness.

The amount of exercise effort these participants could manage was described in units known as Metabolic Equivalent of Task (MET). For instance, five METs is about as strenuous as walking up a flight of stairs. Jogging is equal to about seven METs and walking to about three.

The research team prescribed the patients an exercise program tailored to their age and physical ability, which gradually increased in intensity.

By the end of four years, those who had increased their fitness levels by two METs or more, and those who lost weight were more likely to have reduced or no AF symptoms than those who improved by less than two METs or not at all.

Dr. Michael Lloyd, a cardiologist at Emory University Hospital in Atlanta, Georgia, noted in an email that cardiorespiratory fitness is defined as how much oxygen your heart and lungs can deliver to your muscles.

Though increasing cardio fitness seems to be beneficial, Lloyd, who was not involved in the study, advises caution. “Overweight people should check with their doctor prior to embarking on any exercise program,” he said.

Sanders recommends a tailored exercise program, “in which consideration for age and physical ability should be made so that targets are achieved without risking injuries.”

Dr. Waqas Qureshi, a cardiology researcher at Wake Forest University in Winston-Salem, North Carolina, who also was not involved in the study, noted that weight loss from exercise may add to the protection against heart irregularities.

Lloyd, however, emphasized that cardio fitness is beneficial even apart from weight loss. “If you are overweight, it's not just the pounds that matter, it's how fit you are. This study shows that increasing your fitness through exercise and lifestyle choices does reduce your chance of having the most common arrhythmia.”