How well is the heart performing its job of pumping blood? (Ventricular function is the term cardiologists use to describe the pumping efficiency of the heart.) A cardiologist must be able to answer this question before deciding whether cardiac surgery will be safe or helpful. For example, coronary artery surgery may prolong life in patients with three-vessel disease and mild depression of ventricular function. If ventricular function is normal, bypass surgery will not improve survival; if it is severely depressed, bypass surgery will be too dangerous. In a disease such as myocardiopathy, measurement of ventricular function is often the only way a cardiologist has of knowing that disease is in fact present and how serious it is.

After many false starts and a great deal of research, it is now possible to measure ventricular function very accurately.

The heart pumps about 6 liters of blood a minute. This volume is called cardiac output. Cardiac output is simple to measure, but it isn’t a good index of ventricular function. A patient with a normal cardiac output can still die of heart failure.

Stroke volume is the amount of blood pumped out of the heart with each beat and is easy to calculate using simple arithmetic. If the heart is pumping 6,000 cc of blood per minute and beating 80 times a minute, the stroke volume will be 75 cc. This is a step further but it still doesn’t give an accurate idea of cardiac function.

After many false starts, a reliable measurement of ventricular function has emerged. This measurement is called the ejection fraction. Everyone involved in the care of cardiac patients must know what the ejection fraction is, what the normal values are, and how these values are used (Fig. 23-1).