caused by friction between the visceral and parietal pericardial surfaces. The three components are attributable to the rapid movements of the cardiac chambers. The systolic component is related to ventricular contraction and is the one most commonly heard. There are two diastolic components: one in early diastole resulting from rapid ventricular filling and one late in diastole caused by atrial contraction. The two diastolic components frequently merge, so a two-component rub is most often heard.