Prescribing exercise for your heart is like buying wine for a dinner party. You know it's a good idea, but what kind? How much? The good news: Even a small amount of aerobic activity yields some benefit. The better news: Optimum heart health requires a combination of intense cardio work and mellow endurance sessions—which will pay off on race day as well. Here's what the experts say:

Do Something—Anything!
Work, family, hammocks... All kinds of distractions can thwart your training plans, but don't give up completely. Strive to get at least 30 minutes per day of moderate-intensity aerobic activity. All forms of cardio work do the trick: running, cycling, team sports, swimming, and treadmills and other stationary trainers. No time for a quick workout? Yard work and even riding your cruiser to the office count. A Harvard Alumni Health study found that heart-disease risk starts declining when you burn just 1,000 calories per week (about two hours of running at a ten-minute-per-mile pace).

Step It Up
A rigorous training plan dovetails nicely with a smart heart regimen. Mix intervals into your workouts; they improve your performance at lactate threshold and help train your heart to work more effectively and recover more quickly. Do at least one or two interval sessions weekly, reaching your maximum sustainable heart rate (see "Express Train," above) during three to four high-intensity efforts of up to ten minutes each (adjust for training goals). Slow to a recovery pace between intervals.

Perform endurance workouts at least three times per week. You should be able to maintain a conversation during these moderately paced efforts. Distance will vary. If you're training for a competition, build mileage gradually until you're covering at least 75 percent of your race-day mileage.