Nowadays most medical patients suffer from combined pathology. One of the most frequent examples is a combination of coronary heart disease (CHD) and duodenal ulcer (DL). The pathogenetic interrelations between these diseases have not been fully studied yet. Meanwhile, knowledge of shifts in cardiac rhythm variability (CRV) would widen the concept of the pathogenesis of these diseases, play predictory role, and allow individualization of prophylaxis and treatment. The subjects of this study were 23 patients suffering from CHD and DU. They were compared with 34 DU ulcer patients, and 15 CHD patients. The study revealed that in patients with combined pathology CRV was significantly lower than in those who had either CHD or DU.