the stretching of the muscle fibers augments cardiac muscle contraction by increasing the calcium sensitivity of the myofibrils, causing a greater number of actin-myosin cross-bridges to form within the muscle fibers. specifically, the sensitivity of troponin for binding ca increases and there is an increased release of ca from the sarcoplasmic reticulum. in addition, there is a decrease in the spacing between thick and thin filaments, when a cardiac muscle fiber is stretched, allowing an increased number of cross-bridges to form. the force that any single cardiac muscle fiber generates is related to the sarcomere length at the time of muscle cell activation by calcium. the stretch on the individual fibers, caused by ventricular filling, determines the sarcomere length of the fibres. therefore the force (pressure) generated by the cardiac muscle fibres is related to the end-diastolic volume of the left and right ventricles as determined by complexities of the force-sarcomere length relationship.