During exercise, your heart beats faster to keep up with the increased demands of your body. Specifically, it needs to beat faster in order to pump more oxygen-rich blood to your muscles, including the heart muscle itself. However, a sensation of an abnormal heart beat could potentially be due to an arrhythmia, and it is important for you to be further evaluated by your physician to determine the next best step in your evaluation.
Typically, the sensation of an isolated, intense heart beat is due to premature atrial or ventricular complexes. These are essentially early heart beats that originate within the heart itself but outside its typical electrical conduction system. These are extremely common and typically benign, and situations such as dehydration, exercise, stress, or alcohol or caffeine consumption can increase their frequency. Given your description, this is most likely what is occurring. However, in some instances, these can occur so frequently that it poses a problem for the heart muscle itself. Although your reportedly normal echocardiogram
is reassuring, it is difficult to fully comment on this without the full details, and I urge you to discuss this further with your physician.
In other situations, although you only sense an isolated extra beat, this may in fact be due to an arrhythmia, such as atrial fibrillation, atrial flutter, AV nodal reentral tachycardia, atrial tachycardia, atrioventricular reciprocating tachycardia, or ventricular tachycardia. If your physician suspects these, it is often necessary to perform 24-hour EKG
monitoring or perform an exercise stress test to determine if these can be reproduced by exercise in a monitored setting. Again, I urge you to discuss these possibilities with your physician to determine if any of these additional tests are indicated.