Heart rate increases during inspiration and slows during post-inspiration; this respiratory sinus arrhythmia helps match pulmonary blood flow to lung inflation and maintain an appropriate diffusion gradient of oxygen in the lungs. This cardiorespiratory pattern is found in neonatal and adult humans, baboons, dogs, rabbits and seals. Respiratory sinus arrhythmia occurs mainly due to inhibition of cardioinhibitory parasympathetic cardiac vagal neurons during inspiration. Surprisingly, however, a recent study in anesthetized rats paradoxically found an enhancement of cardiac vagal activity during inspiration, suggesting that rats have an inverted respiratory sinus arrhythmia. To address this controversy this study examined respiratory sinus arrhythmia in conscious freely moving rats, and tested whether the commonly used experimental anesthetics, urethane, pentobarbital or ketamine/xylazine alter respiratory sinus arrhythmia. Heart rate significantly increased 21 beats per minute (bpm) during inspiration in conscious rats, a pattern similar to the respiratory sinus arrhythmia that occurs in other species. However, anesthetics altered normal respiratory sinus arrhythmia. Ketamine/xylazine (87 mg/kg, 13 mg/kg) depressed and pentobarbital (60 mg/kg) abolished normal respiratory sinus arrhythmia. Urethane (1 gm/kg) inverted the cardiorespiratory pattern so that heart rate significantly decreased during inspiration. Our study demonstrates that heart rate normally increases during inspiration in conscious, freely moving rats, similar to the respiratory sinus arrhythmia pattern that occurs in other species, but that this pattern is disrupted in the presence of general anesthetics including inversion in the case of urethane. The presence and consequences of anesthetics needs to be considered in studying the parasympathetic control of heart rate.