the sound heard on cardiac examination is characteristic of a pericadial friction rub with is pathognomonic for pericarditis it is believed to be caused by friction between the vissceral and parietal pericardial surfaces the three components are attributable to the rapjd movment 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 components frequently merge so a two-component rud is most often heard