The objective was to establish whether an intravascular volume increase leads to a heart rate (HR) incerase without increased sympahetic tonus. HR changes at rest and at deep breathing (6/min - simulated increase of atrial filling pressure) were measured in patients after heart transplantation. Evaluation of dependency of HR changes on breathing depth was done through a new time series methodology. The data was evaluated through graphs displaying a significant increase in the graph area at deep breathing, when compared with breathing at rest (p<0.01). We presume that an incease in HR corresponds to increased intravascular volume and malfunctioning kidneys.