The most important task of the heart is to pump oxygen and other important molecules to the rest of the body. Like any other muscle, the efficiency of the heart improves with fitness. Weight is one of the most important indicators of overall fitness, so it is intimately tied to the operation of the heart.
Body Mass Index
Body mass index—or BMI for short—is a ratio of weight to height. It isn't intended as a diagnostic tool, but it does offer a quick and easy calculation that can identify potential weight problems in adults. Depending upon the numbers, individuals can be classified as underweight, normal, overweight or obese.
If you are overweight for your size, according to the National Emergency Medicine Association, you will have a higher overall heart rate. That is because your heart will have to pump harder to supply energy to the body. A higher level of blood pressure is also a corollary of high weight.
Because BMI correlates with weight, it will also therefore correlate with heart rate during exercise. The difficulty that the heart will have pumping blood in the midst of strenuous activity means that it will have to beat faster in individuals with high BMI to meet the needs of the body.
Recovery Heart Rate
Overweight individuals will also have a less responsive heart. The recovery heart rate, or the rate at which your heart beats after strenuous activity, should fall faster if you are in good shape. If you are not in particularly good shape, then your heart rate will take longer to fall.
BMI is not a perfect tool for identifying weight. Because muscle is much denser than fat, BMI cannot distinguish between someone who is overweight and someone who is muscular and has exceptional health. Athletic individuals will actually have a more efficient, responsive heart.