Introduction: This study aimed to investigate ventilatory correlates of conditioned psychoemotional states – responses to fear, anxiety and restful states and heart rate variability. Respiratory, end-tidal carbon dioxide pressure (PetCO2) and heart rate changes were studied in a differential fear and anxiety conditioning paradigm as well as in a restful state paradigm. We aimed to find out which kind of images, evoking a corresponding psychoemotional state, induce changes in respiration, causing hyperventilation and in heart rate variability. Medically unexplained dyspnea refers to a condition characterized by a sensation of dyspnea and is typically applied to patients presenting with anxiety and hyperventilation without underlying cardiopulmonary pathology. We were interested to know how anxiety triggers hyperventilation and elicits subjective symptoms in those patients. Using an imagery paradigm, we investigated the role of fearful imagery in provoking hyperventilation and in eliciting symptoms, specifically dyspnea and heart rate variability as well as the role of restful psychoemotional state. Methods: Twenty-eight patients with medically unexplained dyspnea matched for age and gender were exposed to scripts and asked to imagine both fearful and restful scenarios of images, while end-tidal PCO2 (PetCO2) and breathing frequency were recorded and subjective symptoms evaluated. The subject who had PetCO2 falling more than 5 mmHg from baseline and persisting at this low level for more than 15 seconds in the imagination was regarded as a hyperventilation responder. Parallel was registrated cardiac activity. Results: In patients with medically unexplained dyspnea, imagination of fearful scenarios, induced anxious feelings, and provoked a significant fall in PetCO2 (P<0.05). Breathing frequency tended to increase. 18 out of 28 patients were identified as hyperventilation responders compared to 8 out of 28 normal subjects without hyperventilation(P<0.01). The patients reported symptoms of dyspnea, palpitation or rapid heart beat in the same fearful script imagery. Additionally, PetCO2 fall was significantly correlated with the intensity of dyspnea and palpitation experienced during the mental imagery on one hand, and with anxiety symptoms on the other. Restful scenarios of images induced also hyperventilation but in comparison fearful scenarios of images they differ qualitative. Heart rate variability changed in case of hyperventilation in correlation with restful scenarios of images. Conclusions: Fearful imagery provokes hyperventilation and induces subjective symptoms of dyspnea and palpitation in patients with medically unexplained dyspnea. Restful imagery provokes hyperventilation and induces changes in heart rate variability by increasing. The difference between the both hyperventilatory states is that in case of fearful imagery we observe tachypnoe and in case of restful imagery – hyperpnoe.