Quantitation of regional ventricular wall properties is critical to determining the contribution of regional loading and contractility to ventricular function. Regional changes may affect global function by altering loading or coronary flow in distant areas. No methods are currently available for accurately determining regional properties, so that it is not possible to determine whether abnormal pump or regional shortening function is due to altered loading or to abnormal contractility. The objective of this proposal is to test the hypothesis that transverse deformational properties of ventricular muscle correlate with characteristics in the plane of the muscle, such as ventricular stiffness. This hypothesis is based on the observation that compressability of muscle correlates with its stiffness, and on a simple spring model that predicts that there are relationships between muscle properties in orthogonal directions. Isolated, beating animal septums will be mounted in a servo system where biaxial force and displacement measurements in the plane of the muscle can be continuously performed, and loading conditions can be continuously changed. A measuring system will be developed by which the septa can be deformed transversely and compressing force and displacement can be measured while the septum is biaxially strained in its plane. Relationships derived from the force and displacement data in the plane of the ventricular wall can be directly compared with those from the transverse measurements for testing of the hypothesis. The determination of the relationships between ventricular wall properties transverse and in the plane of the wall will allow the determination of regional wall stiffness by "poking" the septum perpendicular to its wall. Differentiation of loading from contractility has important clinical implications where abnormal function may be due to abnormal loading or contractility. The measurement of systolic stiffness would allow the determination of both contractility and systolic loading, while the measurement of diastolic stiffness would allow determination of diastolic loading.