A friction rub characteristic of pericarditis is composed of several components, the typical friction rub having two or three. The first part (provided the rhythm is normal sinus) is related to atrial systole, resulting in a friction component in presystole. The second component is related to ventricular systole, producing a systolic friction rub. The third component generally occurs in the early to middle phase of ventricular diastole, apparently coincident with the time of rapid filling. Sometimes only two components are heard which may be related to atrial systole and ventricular systole. If the rhythm is irregular with atrial fibrillation (thereby having no atrial component), a friction rub having two parts is produced in ventricular systole and diastole. As a practical rule, one should hesitate to make a diagnosis of acute pericarditis after hearing only one friction component in systole, although occasionally it may represent an early finding of pericarditis with the diastolic component appearing subsequently. The auscultatory results in pericardial effusion and constrictive pericarditis are discussed.