Thirty-three captive leopard cats, Leopardus tigrinus, were anesthetized with xylazine (1–2 mg/kg) and ketamine (10 mg/kg), and electrocardiograph (ECG) tests were recorded in all leads with 1 cm  =  1 mV sensibility and 25 mm/sec speed repeating DII lead at 50 mm/sec speed with the same sensibility. Results expressed by mean and standard deviation were: heart rate (HR)  =  107 ± 17 (bpm); P-wave  =  0.048 ± 0.072 (s) × 0.128 ± 0.048 (mV); PR interval  =  0.101 ± 0.081 (s); QRS compound  =  0.053 ± 0.012 (s) × 1.446 ± 0.602 (mV); QT interval  =  0.231 ± 0.028 (s); R-wave (CV₆LL)  =  1.574 ± 0.527 (mV); R-wave (CV₆LU)  =  1.583 ± 0.818 (mV); heart rhythm: normal sinus rhythm (15.2%), sinus rhythm with wandering pacemaker (WPM) (60.6%), sinus arrhythmia with WPM (24.2%); electric axis: between 30° and 60° (6.1%), 60 (6.1%), between 60° and 90° (57.6%), 90° (9%), between 90° and 120° (21.2%); ST segment: normal (75.7%), elevation (18.2%), depression (6.1%); T-wave polarity (DII): positive (100%); T-wave (V₁₀): absent (6.1%), negative (63.6%), positive (18.2%), and with interference (12.1%). Through ECG data comparison with other species, unique features of Leopardus tigrinus' (leopard cat) ECG parameters were detected. Some of the study animals presented with an R-wave amplitude that was indicative of left ventricle overload according to patterns for normal domestic cats (Felis cati). Echocardiographic exams revealed normal heart cavities' function and morphology. The aim of this study was to establish some electrocardiographic parameters of captive L. tigrinus.