OBJECTIVE Was to estimate an influence of acute cellular rejection on electrophysiologic parameters of allograft and remnants of recipient's heart, in patients after orthotopic heart transplantation (OHT). METHODS Analysis was performed in 25 OHT recipients (24M/1F, age 48.4 +/- 9 y., ischemic time 197 +/- 51 min., donor age 30 +/- 9 y.), who underwent electrophysiological study (EPS), along with elective endomyocardial biopsy (EMB), scheduled for the 1st month after the surgery. Results of EPS were correlated with a degree of rejection, assessed with the ISHLT grading system. Grades > or =3A were considered a significant cellular rejection. RESULTS ISHLT grade 0 was observed in 8 patients, grade 1A or 1B in 12 patients, and 3A in 5 patients. Frequency of transplanted heart rhythm (TH-R) was 691.3+/- 37 ms in patients with ISHLT grade 0, 690.4 +/- 41 ms in patients with grade 1A or 1B, and 744.4 +/- 668 ms in individuals with 3A rejection (p < 0.04, for difference between 0 and 3A groups). Intraatrial conduction time (IntrtaCT) was significantly shorter in grade 3A group (20.4 +/- 1.6 ms), when compared with patients without rejection (36.2 +/- 4.9 ms, p < 0.03), or with 1A or 1B rejection (41.5 +/- 13 ms, p < 0.032). Also interatrial conduction time (InterCT) was the shortest in patients with 3A rejection (53.8 +/- 4.3 ms), when compared with ISHLT grade 0 group (78.5 +/- 7.6 ms, p < 0.02) and 1A/1B group (74.1 +/- 12 ms, p < 0.023). The other characteristics of atria, ventricles and AV-junction performance were comparable in all patients. CONCLUSIONS TH-R, IntraCT and InterCT should be considered as the markers of significant cellular rejection in patients after OHT. Further analysis involving higher number of patients is warranted.