We have previously demonstrated that cardiac myocytes isolated from the hearts of adult dogs develop rapid repetitive cytosolic Ca² transients, membrane depolarization, and cell contraction by mobilization of sarcoplasmic reticulum Ca² stores when exposed to a soluble factor from the trypomastigotes of Trypanosoma cruzi. These findings led us to investigate the regulatory mechanisms of cytosolic Ca² in cardiac tissues from dogs chronically infected with T. cruzi. Expression of the plasma membrane calcium pump (PMCA) RNA and protein was determined by Northern and Western blotting, respectively, followed by densitometric analyses. A 642-bp PMCA 1b complementary DNA probe derived from canine epicardial tissue hybridized to 2 major transcripts (7.3 and 5.3 kb) in canine epicardium. Expression of the dominant transcript (7.3 kb) was 77% greater in cardiac tissues obtained from dogs with chronic T. cruzi infection (140 days after inoculation) in comparison with constitutive expression levels in normal dogs. Monoclonal antibody 5F10, known to recognize all isoforms of the PMCA, was used to detect expression of the PMCA protein in epicardial tissue. Expression of a 142-kDa protein was increased by 58% in the cardiac tissues of infected dogs when compared with those from uninfected dogs. To establish a link between the upregulation of PMCA in dogs chronically infected with Chagas disease and the ventricular-based arrhythmias and myocardial failure that occur during this stage of disease both in dogs and humans, further study will be required.