Impedance cardiography proved valuable to estimate the stroke volume and other cardiac parameters noninvasively, when the electrical resistivity of the blood was corrected with hematocrit. 2. Cardiac response to graded exercise on a bicycle ergometer up to the maximal load in healthy young and active middle-aged subjects was divided into four phases from the changes in cardiac parameters such as stroke volume, cardiac output, ejection index and height of the atrial wave. 3. The ischemic patients did not tolerate well the exercise after the second phase or drift phase of exercise. 4. Physical training enhanced the cardiac function in work through increase in cardiac output and work load.
