We collected tissue samples from the left ventricular myocardium in 20 patients with aortic regurgitation, examined the correlation between myocardial ultrastructure and cardiac function at rest and obtained the following results. The extent of fibrosis in the myocardium and ultrastructural changes in the myocardial cells were respectively expressed in LM-Score and EM-Score. Furthermore, the myofibril changes expressed by the EM-Score were added to the LM-Score (Myo＋LM-Score), and each score was calculated and compared with the parameters of cardiac function. There was no significant correlation between EM-Score and parameters of cardiac function. LM-Score was correlated with Max dv/dt at r＝－0.471 (p<0.05) and with endodiastole (D/L) at r＝－0.567 (p<0.01) significantly, showing a negative linear correlation. Myo＋LM-Score was correlated with EF at r＝－0.574 (p<0.01) and with△ D at r＝－0.577 (p<0.01) significantly, showing a negative linear correlation. Among the cardiac functions at rest in patients with AR, the morphologic and diastolic parameters were closely related with the extent of fibrosis, and the contractility was closely related both with a change in myofibrils and with the extent of fibrosis. Thus, the cardiac functions at rest in patients with AR were correlated with the myocardial factors.