RESUMEN
INTRODUCTION AND OBJECTIVES: Physical exercise causes a significant increase in the incidence of cardiac arrhythmias in athletes, basically when maximal capacity is approached and during the period of early recovery. In this study the incidence of cardiac arrhythmias consecutive to maximal exercise (sprint) was studied using racing greyhounds as a biomodel. METHODS: The study was done on 399 greyhounds taking part in programmed speed races at a greyhound track. For each animals two electrocardiograms where taken: the first before the race and the second between 90 and 150 seconds after finishing it. RESULTS: 112 cases of abnormal arrhythmias were found, 32 before racing, and 80 afterwards. Of these 80 post-effort cases, 80% did not present any abnormalities in cardiac rhythm before racing. Only cases of electrical alternans, electrical alternans + sinus tachycardia, ventricular extrasystoles, sinus tachycardia and ventricular tachycardia were due to non-random phenomena. CONCLUSIONS: Maximal physical exercise (sprint) provokes a significant increase (150%) in the incidence of abnormal cardiac arrhythmias during the period of early recovery: mainly electrical alternans, ventricular extrasystoles, sinus tachycardia and ventricular tachycardia. The class, sex, age, weight of greyhound and distance covered do not have a significant influence on the presentation of arrhythmias, except in cases of sinus tachycardia and distance.