Isovolumetric relaxation and diastolic stiffness of the left ventricle were studied in seven open-chest dogs following serial ligation of coronary arteries. After experimental infarction, diastolic stiffness increased by 221% (pmln (p< 0·001). Since relaxation velocity is dependent on afterload, two essentially pressure-independent relaxation parameters were introduced, dp/dtmln/left ventricular end-ejection pressure (LVEEP) and the time interval, in which relaxation is half completed (Tp/2). These parameters displayed a 25% and 29% decreased ability, respectively (p<0·01), of relaxation after coronary artery ligation. An approximately exponential relationship existed between diastolic stiffness and relaxation ability. It is concluded that changes in the elastic wall properties influence the diastolic stiffness and the relaxation ability of the left ventricle. The slowed relaxation influenced coronary blood flow, so that after coronary ligation left ventricular circumflex flow during the relaxation phase was impaired by 14% and left coronary circumflex diastolic inflow index decreased by 24%.