A good brisk walk is enough to strengthen your heart, researchers have found.
Some experts believe that only strenuous activity has any beneficial effect.
But a study of obese adults found moderate exercise was enough to raise the heart beat to recommended levels.
The researchers, from the University of Massachusetts, Boston, reported their findings at a meeting of the American Heart Association.
Advisory groups recommend that exercise must push the heart rate up to at least 55% of its maximum to have any positive impact.
Many believe that vigorous exercise is the only way to do this - but the latest study suggests this is not necessarily true.
Rather than the old adage that there is "no pain, no gain", they believe that "if the pace feels right, it probably is".
Lead researcher Professor Kyle McInnis said: "A large segment of the population still believes exercise must be vigorous, demanding or involve more complicated activities than walking to adequately raise one's heart rate.
"This perception of 'no pain, no gain' can discourage people from starting to exercise at all."
The researchers studied 84 obese adults who were seeking professional advice on a safe level of exercise.
At the first visit, researchers measured heart rate and oxygen use, while the subjects walked on a treadmill with a gradually increasing steepness until they felt tired.
On a different day, the subjects walked one mile on the treadmill with instructions to maintain a "brisk but comfortable" pace.
Participants completed the walk in an average of 18.7 minutes, at an average speed of 3.2 miles per hour.
During the self-paced walk, all the participants achieved the recommended levels of exercise intensity, based on their previous heart rate measures.
Thirteen were at moderate intensity (55-69% of maximum heart rate), 58 at hard intensity (70-89%) and 13 at very hard intensity (90-100%).
Professor McInnis said: "Comparison with the treadmill tests showed that when participants self-selected a speed that was comfortable but brisk, their heart rate and level of exertion was in a safe range but high enough to improve their cardiovascular fitness.
"You really can get your heart rate up to the level that your doctor would recommend, and you don't have to jog or run to do it."
Forget the gym
Dr Kevin Channer, a consultant cardiologist at the Royal Hallamshire, told BBC News Online he was concerned that many people thought it was too tough to try to get fit.
"If you do nothing at all then your cardiovascular risk is higher than somebody who takes exercise, but if you are obsessive about exercise and run for 15 miles every day, then your risk starts to rise again," he said.
"Being healthy isn't difficult. People don't need to play sport or go to the gym, they simply need to get out of their cars and go for a walk."
Dr Hugo Crombie, of the Health Development Agency, said everybody should try to take a minimum of 30 minutes moderate activity on at least five days of the week.
He said: "Walking is excellent exercise - not only does it provide the sort of activity to benefit health but it does not need any special skills, equipment or access to a gym.
"The evidence shows that people can be encouraged to walk more and that this increase can be maintained over the years."
A British Heart Foundation cardiac nurse said: "Brisk, regular walking is the ideal way for people to get the exercise they need to benefit their health: it's free and easy for most people to fit into their daily life and can influence weight loss, blood pressure, diabetes and cholesterol levels.
"It also provides a cardiovascular workout without putting too much strain on the heart."