Every day you need to do something that specifically makes your heart work harder and beat faster. Not only does exercise strengthen the heart muscle, it causes blood vessels to dilate and expand, which helps them retain their elasticity. If you’re sedentary, they'll become rigid and hard; and when you need them (like during a stressful situation), they won't be able to do their job. That's when heart attacks strike.
For real cardiovascular benefits, you have to increase your pulse rate up from its normal working rate and keep it up long enough for your blood vessels to dilate. Almost any exercise can be beneficial—walking, swimming, riding a bike, jogging in place.
It doesn't have to be intense, but it needs to be on a regular basis. In fact, occasional "Iron Man" strenuous workouts are far less effective than simply walking each day.
In one study, climbing 50 or more steps a day (at one time) reduced heart disease by 20 percent. Walking as little as five blocks a day reduced it by 21 percent, and regular vigorous sports activity dropped risk by 27 percent. In another study of 30 men, walking as little as 20 minutes daily showed positive LDL reductions.