This study was carried out to investigate the effects of age, sex and season change on electrocardiograms of Van cats. Thirty-eight (male and female) healthy Van cats, 3-15 months old were used. Electrocardiograms (ECGs) and heart radiographs were obtained from cats seperately in summer, autumn, winter and spring. ECGs were recorded as bipolar, augmented unipolar and precordial leads (CV6LL, CV6LU, V-10). Durations and amplitudes of waves on the trace were measured in lead II and the electrical axis also measured in leads I and III. Radiographic examination was performed in the right lateral recumbency position (covering the whole thoracic cavity) and the dose of the X-ray beam was 44-47 kV. The duration of P wave was 0.04 s. and its amplitude was 0.10 mV-0.12 mV. The PR interval was 0.06-0.08 s. The duration of the QRS complex was 0.03-0.04 s and its amplitude was 0.16 mV-0.5 mV. The duration of the T wave was 0.06-0.09 s. and its amplitude was 0.1 mV-0.15 mV. The duration of the QT interval was 0.15-0.18 s. The T wave was negative in all of the aVR leads and in some of leads 11, aVL and V4. The mean electrical axis of the cats was +66.5degrees to +87.5degrees. No significant differences were seen among the groups. The heart rate in the first group was determined by seasons to be 200 +/- 12(a), 170 +/- 5.9(b), 193.2 +/- 12(a) and 207.2 +/- 15(a) beat/min (a,b: P < 0.05); in the second group 201 +/- 8.7, 179.8 +/- 5.1, 202.8 +/- 14 and 195.6 +/- 5.2 beat/min; in the third group 176.2 +/- 7.7, 170 +/- 7, 186.6 +/- 13 and 193.5 13 beat/min; and in the fourth group 186.3 +/- 16, 180 +/- 14, 200 +/- 11 and 210 +/- 15 beat/min, respectively. According to radiographic examinations. the heart was located 4(th) - 7(th) and 5(th) - 7(th) intercostal intervals.