A new model for the pressure relaxation of the left ventricle is proposed. The model presumes that the myocardium relaxes asynchronously, but that when regions begin to relax, after a delay, the local wall stress decays as a mono-exponential process. This formulation results in an apparently bi-exponential process (two time constants) which has been previously reported. It is shown that the ratio of the two time constants (T2/T1) can be interpreted as the fraction of the myocardium which relaxes synchronously. Data are presented illustrating the Model during transient coronary occlusion in patients undergoing percutaneous transluminal coronary angioplasty.