Artificial ventilation (AV)-associated pneumonias are the most common infectious complication in cardiosurgery. This prospective comparative study covered 50 patients with AV-associated pneumonias occurring after surgery under extracorporeal circulation (EC). All the patients received the routine perioperative antibiotic prevention regimen (cefuroxime or ceftriaxone). According to the initial therapy, the patients with evolving pneumonia, the patients were divided into 2 groups: 1) those were given cefuroxime (maxipim); 2) those receiving a combination of maxipim or clarithromycin (clacid). The analysis has indicated that if pneumonia develops after surgery under EC, then this most frequently occurs in the first 5 postoperative days, i.e. early AV-associated pneumonias are prevalent. In cases of concurrent pneumonia, the duration of EC, the length of stay in an intensive care unit, and the total period of hospi- talization considerably increase. For cardiosurgical patients, the laboratory guide for establishing the diagnosis of AV-associated pneumonia is the elevated blood cell levels of more than 15 x 10(9)/l, unlike those of more than 10 x 10(9)/l proposed for most patients. The etiology of AV-associated pneumonia is shown to vary with the timing of complication occurrence. There is evidence for the involvement of intracellular microorganisms (Chlamydia, Mycoplasma) in the development of early AV-associated pneumonias in at least every 10 patients. The advantages of a study of bronchoalveolar lavage samples over that of endotracheal aspirates for the etiological diagnosis of pneumonias were revealed. The advisability of prescribing a combination of a beta-lactam antibiotic (third- or fourth-generation cephalosporin) and a macrolide (clarythromycin) in early AV-associated pneumonias is warranted. The objective criterion for the adequacy of this combination is positive changes in the marker of severe bacterial infections (procalcitonin). An algorithm is offered for antibacterial therapy for AV-associated pneumonias developing after cardiosurgical operations, which considers the performed antibiotic prevention and the timing of pneumonia development.