This manuscript aims to provide a simple and concise discussion on heart rate variability (HRV) for small animal veterinarians. Despite the fact that heart rate variability analysis techniques have been used for quite a long time in medical sciences, it seems to be not completely understood by a large fraction of veterinarian professionals, thereby, reducing the possible benefits to patients that could arise from such information. The analysis of the R-R intervals enables the veterinarian to evaluate autonomic sympathetic and parasympathetic modulation of the heart, composing the so-called cardiac autonomic balance. Several pathophysiological states lead to profound changes in autonomic balance, especially in the cardiovascular system. Therefore, heart rate variability methods remain a valuable and powerful tool for the diagnosis and prognosis of cardiovascular diseases.