An important qualifier is whether the palpitations-the sensation of abnormal, fast, or irregular heartbeats-occur during exercise or afterwards. In general, palpitations while youre exercising could be concerning, especially if they are associated with chest discomfort, severe shortness of breath, or lightheadedness. Such symptoms would suggest that a stress test is indicated, both to assess for coronary artery blockages, as well as for the type of heart rhythm causing your palpitations. Conversely, palpitations which occur after exercise (or happen at rest and resolve during exercise) are generally not worrisome. Such symptoms usually stem from benign premature atrial contractions (PACs) or premature ventricular contractions (PVCs). Take your pulse, as you may sense palpitations, but be in a normal rhythm. If your doctor feels it is indicated, you may be advised to try a portable 24- or 48-hour modified EKG to further analyze your palpitations.