The warmer weather and longer days of summer are great inducers to be outdoors and be active. In addition to being fun, maintaining an active physical routine can also keep you heart healthy by reducing your risk of heart disease, improving your blood cholesterol levels and preventing and managing high blood pressure. And the health advantages of staying physically active don't end there. Maintaining a regular exercise routine can also help you stay at a healthy weight, prevent bone loss, increase muscle strength, raise energy levels and manage stress.

The American Heart Association recommends that healthy adults under age 65 should aim for 30 minutes of moderate-intensity activity a day, five days a week and do eight to ten strength-training exercises, eight to 12 repetitions of each exercise, twice a week. (Moderate-intensity activity means exercising hard enough to raise your heart rate and break a sweat, but still be able to carry on a conversation.) And you don't have to do all 30 minutes at once. Research is showing that moderate-intensity physical activity in ten-minute bouts, three times a day is just as effective as getting in all your exercise in one 30 minute routine.

Before starting any exercise program, be sure to check with your doctor to discuss which types of exercise are best for you.

Here are four heart-healthy activities that will increase your heart rate, help you burn calories and keep you outdoors this summer.

1. Bicycling. Whether it's outdoors or indoors on a stationary bike, bicycling is a great way to stay fit. Using your legs to peddle a bike enables you to increase endurance while burning lots of calories-as much as 250 to 500 calories in 30 minutes, depending on your speed and level of resisance.

2. Walking. Especially when it's done briskly, walking burns about 180 calories in 30 minutes and even more if you include hilly areas or add a few minutes of jogging to your routine.

3. Rowing. Vigorous rowing can really get your heart rate pumping, while giving your arms a good workout, too. Plus, rowing is a good way to burn lots of calories in a short amount of time. For example, a 145-pound person can expend about 300 calories in just 30 minutes.

4. Swimming. This is a great aerobic sport that gives your whole body a workout. And the more body parts you use, the more calories you'll burn. For example, doing the breaststroke for 30 minutes will burn about 400 calories. Plus, swimming is easy on your joints.