Hi Rainbow,   Here is a link to information on arrhythmia (irregular heart beat) - http://www.healthcentral.com/heart-disease/patient-guide-44628-6.html.  Sinus tachycardia is a rapid heart beat due to irregularity with the electrical impulses sent from the sinus node.  The link above will better explain the sinus node and the link to heart rate.  Sinus tachycardia is typically defined as a heart rate greater than 100 beats per minute.  The average adult heart rate is around 70 beats per minute.  The better your physical condition the lower your heart rate (usually).   Here's a link on tachycardia (fast heart beat) -http://www.healthcentral.com/encyclopedia/408/729.html   The Joint National Committee defines four blood pressure categories.  A blood pressure less than 120/80 mm Hg falls within the normal range.   All the best, Lisa Nelson RD Heart Healthy Tips