The leading cause of death in the United States is cardiovascular disease (otherwise known as heart disease). The tragedy is that many of these deaths are both premature and preventable. So what's the most effective way to improve heart health and avoid becoming a statistic? Aerobic exercise. Still, many seem confused about what to do. "How much is enough?" and "what kind is best?" are two of the most common questions people ask. Here are some parameters, but remember to speak with your healthcare provider before beginning any new fitness routine.

How much is enough?

Healthy adults between 18 and 65 should aim for 150 minutes a week of moderate-intensity aerobic activity, a guideline supported by the American Heart Association, American Council on Exercise, and the American College of Sports Medicine. That's not as much as it sounds like if you break it into 30-minute sessions of activities such as walking, riding your bike, or gardening and other yard work. You're working hard enough to meet this recommendation if you break a sweat and feel your heart beating a little faster than normal; you should still be able to carry on a conversation.

On the days you'd prefer to exercise for less time, just work harder. Swim laps, jog, or play basketball for 20 minutes, three times a week and do eight to 10 strength-training exercises twice a week.

Read more about starting a strength-training exercise regimen.

What kind is best?

The best kind of exercise is the kind you will do. If you shudder at the thought of running, walk. If swimming laps sounds as appealing as a root canal, try water aerobics. At the gym, try alternating the cardio machines every few weeks (or doing 10 minutes each on several different machines) so you don't get bored.

Once you have a solid base, add intervals.

The human body adapts amazingly well, and quickly, to the stress of exercise. So once you are consistently exercising and can do so for at least 30 minutes at a time, try adding some interval training into your routine. Just mix some short bursts of effort into whatever you're already doing. It's a great way to get more out of your workouts without making them longer.  

Consider some research published in the Journal of Applied Physiology: Researchers tested the effects of interval training on women in their 20s. They monitored eight women of varying fitness levels as the subjects rode stationary bikes in intervals that alternated between hard and easy efforts. The four-minute bursts of 90 percent effort were followed by two minutes of rest; the women did 10 sets at each session and trained every other day for two weeks. At the end of the training period the amount of fat they burned during one hour of continuous moderate cycling increased by 36 percent, and their cardiovascular fitness increased by 13 percent.

The takeaway message: Just one or two interval sessions per week are all it takes to see a real benefit. Intervals can be slowly incorporated into any existing routine. If you walk for exercise, after a five-minute warm-up increase your speed to a very brisk pace for two to four minutes and then slow down to your normal pace for the same amount of time. Alternate between hard and easy for about 10 minutes.