A method of using CPAP equipment to sense cardiogenic oscillations (48) in a patient's airflow (44), and to monitor and treat the patient's cardiac condition. The apparatus diagnoses cardiac morbidity conditions, such as the existence of arrhythmias or other cardiac abnormalities, and influences and optimized cardiac stroke volume. The apparatus further monitors pulse-transit time, changes in the heart pre-ejection period, and the duration of the cardiac cycle.