If you can improve and strengthen just one muscle in your body, make it your heart. It's your body's largest, and, frankly, if it lets you down, you're not going to be spending a lot of time worrying about the size of your abs or biceps.

Before you embark upon a regular routine of heart-strengthening cardiovascular exercise, you must first determine your maximum heart rate. The most accurate way to do this is via a doctor-administered stress test. You will wired up to a heart monitor and set loose upon a treadmill, in increments of advancing intensity. The intensity is gamed via increasing the incline and speed of the treadmill. Intensity continues to increase until you become too tired to continue, elect to stop, or your heart rate will not go any higher. That final number is recorded as your maximum heart rate.

The more common approach that the average gym rat uses to get the same approximate number is to subtract her age from 220. Your 40 years old? Figure your maximum heart rate is 180 beats per minute. Pretty simple. This calculation is premised upon the fact that as you age, your maximum heart rate decreases.

Now, let's use that knowledge to build a stronger heart. In short, you will want to elevate your heart rate to between 60 and 90 percent of its maximum rate (intensity) for a minimum of 30 minutes (duration), three days per week (frequency). Longer duration and higher frequency is better, but a greater intensity? Not so much. Your maximum training heart rate for improving aerobic performance should be around 90 percent of your overall maximum heart rate.

By definition, there is no way to exceed your maximum heart rate. According to Dr. Carol Otis and Roger Goldingay, authors of The Athletic Woman's Survival Guide, it is extremely difficult to damage a healthy heart by exercising at or near the maximum heart rate. If that were the case, elite athletes would be suffering heart damage on a regular basis. Your other muscles will likely run out of energy and force you to stop before you have the chance to damage your heart.”

In order to track your heart rate and be certain that it stays “in the zone,” you may find a heart rate monitor useful. Many treadmills have heart rate monitors built-in to the handlebars, but these are of varying and often dubious accuracy.

Although you may be in a hurry to slurp down that post-workout protein probiotic peach smoothie at your gym's Energy Bar, take time to cool down first. The National Academy of Sports Medicine recommends you slowly decrease the intensity of your cardiovascular workout to 40-50 percent of your maximum heart rate for a period of 5 to 10 minutes. This will prevent blood from pooling in your lower extremities, which can lead to dizziness or nausea.