A cardiac function curve is a curve depicted from data on different values of ventricular end-diastolic pressure and the corresponding ventricular beat volume or work per beat.
The cardiac function curve is divided into three segments:
1. Left ventricular end-diastolic pressure in the range of 5 to 15 mmHg is the ascending branch of the curve, and as ventricular end-diastolic pressure increases, ventricular work per beat also increases.
2. Left ventricular end-diastolic pressure in the range of 15-20 mmHg, the curve tends to flatten.
3. When the left ventricular end-diastolic pressure exceeds 20 mmHg, the curve is flat or even mildly downward sloping, indicating that the left ventricular end-diastolic pressure exceeds 20 mmHg and the work-per-excursion is still unchanged or mildly reduced.
The cardiac function curve is used to evaluate the effect of ventricular end-diastolic pressure (ventricular end-diastolic volume), that is, ventricular preload or myocardial initial length, on myocardial contractility.