1. An increase in length in isolated animal muscles causes an immediate increase in contractile force, which is followed by a slower further progressive increase: the slow component. However, the pressure-volume concept, used in characterizing left ventricular function, is dependent on a constant relationship between pressure and volume.
2. We therefore examined the possible occurrence of the slow inotropic component of the response to cardiac muscle stretch in man at cardiac catheterization.
3. Human subjects undergoing left heart catheterization for clinical indications were studied. The development of the slow component was studied by measurement of rate of rise in left ventricular developed pressure and the time course after an increase in end-diastolic volume.
4. No evidence for any slow component was elicited.
5. It is concluded that the slow component of force (or pressure) increase after an increase in cardiac muscle length (or volume) does not have a role in the human heart in situ.