Abnormal cardiac output Abnormal cardiac index 2021-01-15T12:50:05Z Any deviation from the normal value of the cardiac index, defined as cardiac output divided by body surface area. Cardiac output (CO) can be further broken down as the product of stroke volume (SV), which is the blood volume ejected by one heartbeat, and heart rate (HR), which is the number of heartbeats per minute. Therefore, the cardiac index can be defined as Cardiac Output / Body Surface Area = (Heart Rate * Stroke Volume) / Body Surface Area.