Bartonella species (typically B quintana or B. henselae) are an important cause of culture-negative endocarditis. The disease's manifestations are similar to those of subacute endocarditis of any etiology (Chap. 80. Infective Endocarditis). Even if incubated for prolonged periods (up to 6 weeks), blood cultures are positive in only ~25% of cases. Serologic or PCR testing for Bartonella in cardiac valve tissue can help establish the diagnosis in pts with negative blood cultures.