This study presents the electrocardiogram findings from 97 captive tufted capuchin monkeys (Cebus apella) at the São Paulo Zoo (São Paulo, Brazil) while under ketamine anesthesia. The results did not differ greatly from data of domestic carnivores or other studied primate species. The most common rhythm recorded was normal sinus rhythm, followed by normal sinus rhythm with wandering pacemaker. Electrical axis varied from 0° to −150° but was most commonly between 60° and 90°. QRS complexes were predominantly positive in leads DI, DII, DIII, and AVF. These findings allow for the recognition of abnormal rhythms in these primate species and can contribute to future investigations into the cardiovascular diseases routinely diagnosed in primates and humans.