Premature atrial contractions (PACs) are a type of premature heart beat, irregular heart beat or benign arrhythmia which start in the upper two chambers of the heart, also calle atria. These aren't as serious as a Premature Ventricular Contraction (PVCs) and usually require no medical care. Individuals with the condition may report feeling that his or her heart "stops" after a symptom. PVCs and PACs are also sometimes called heart palpitations.