Sinus rhythm is the term used to refer to a normal heart beat pattern on an EKG. There are six distinct features, each identified by a letter from P to U: * P wave - a short upwards "hill" followed by a flat section, representing the contraction of the atria * Q wave - a short sharp drop where the impulse passes the septum between the atria and the ventricles * R wave - a very large and sharp straight rise to a peak well above the flat section of the P wave, representing the contraction of the major ventricles * S wave - a sharp drop to the lowest point, followed by a sharp slight rise, representing the passage of the contraction out of the heart * T wave - a plateau followed by a "hill" larger than that of the P wave dropping down to the plateau, representing the relaxat