The autonomic nervous system is critical for regulating cardiovascular physiology. The neurocardiac axis encompasses multiple levels of control, including the motor circuits of the sympathetic and parasympathetic nervous systems, sensory neurons that contribute to cardiac reflexes, and the intrinsic cardiac nervous system that provides localized sensing and regulation of the heart. Disruption of these systems can lead to significant clinical conditions. Recent advances have enhanced our understanding of the autonomic control of the heart, detailing the specific neuronal populations involved and their physiologic roles. In this review, we discuss this research at each level of the neurocardiac axis. We conclude by discussing the clinical field of neurocardiology and attempts to translate this new understanding of neurocardiac physiology to the clinic. We highlight the contributions of autonomic dysfunction in prevalent cardiovascular diseases and assess the current status of novel neuroscience-based treatment approaches.