A system for improving heart rate coherence of a subject, the system comprising: a pressure generator configured to generate a pressurized flow of breathable gas for delivery to the airway of the subject; sensors configured to generate output signals conveying information related to: i) one or more gas parameters of the pressurized flow of breathable gas, and ii) a heart rate of the subject, one or more processors configured to execute processing modules, the processing modules comprising: a control module configured to adjust levels of one or more gas parameters of the pressurized flow of breathable gas to provide breathing cues to the subject that prompt to transition between breathing phases; a respiratory parameter determination module configured to determine a breathing rate and breathing phases of the subject based on the generated output signals; a coronary parameter determination module configured to determine a heart rate variability for the subject, wherein the heart rate variability is based on the heart rate of the subject; and a target module configured to determine a target breathing rate range and target breathing phases for which the heart rate variability is phase-aligned with the breathing rate and breathing phases of the subject, wherein the control module adjusts the levels of one or more gas parameters of the pressurized flow of breathable gas to guide the subject to breathe according to the determined target breathing phases and within the determined target breathing rate range. a pressure generator configured to generate a pressurized flow of breathable gas for delivery to the airway of the subject; sensors configured to generate output signals conveying information related to: i) one or more gas parameters of the pressurized flow of breathable gas, and ii) a heart rate of the subject, i) one or more gas parameters of the pressurized flow of breathable gas, and ii) a heart rate of the subject, one or more processors configured to execute processing modules, the processing modules comprising: a control module configured to adjust levels of one or more gas parameters of the pressurized flow of breathable gas to provide breathing cues to the subject that prompt to transition between breathing phases; a respiratory parameter determination module configured to determine a breathing rate and breathing phases of the subject based on the generated output signals; a coronary parameter determination module configured to determine a heart rate variability for the subject, wherein the heart rate variability is based on the heart rate of the subject; and a target module configured to determine a target breathing rate range and target breathing phases for which the heart rate variability is phase-aligned with the breathing rate and breathing phases of the subject, a control module configured to adjust levels of one or more gas parameters of the pressurized flow of breathable gas to provide breathing cues to the subject that prompt to transition between breathing phases; a respiratory parameter determination module configured to determine a breathing rate and breathing phases of the subject based on the generated output signals; a coronary parameter determination module configured to determine a heart rate variability for the subject, wherein the heart rate variability is based on the heart rate of the subject; and a target module configured to determine a target breathing rate range and target breathing phases for which the heart rate variability is phase-aligned with the breathing rate and breathing phases of the subject, wherein the control module adjusts the levels of one or more gas parameters of the pressurized flow of breathable gas to guide the subject to breathe according to the determined target breathing phases and within the determined target breathing rate range.