Cardiac muscle cell fatigue. There are two types of cells within the heart: the cardiomyocytes and the cardiac pacemaker cells. Cardiomyocytes make up the atria (the chambers in which blood enters the heart) and the ventricles (the chambers where blood is collected and pumped out of the heart). These cells must be able to shorten and lengthen their fibers and the fibers must be flexible enough to stretch. These functions are critical to the proper form during the beating of the heart. Cardiac pacemaker cells carry the impulses that are responsible for the beating of the heart. They are distributed throughout the heart
Heart failure with preserved ejection fraction and lower ejection fractions. Cardiac output is dependent on stroke volume and heart rate. A significant portion (55-77%) of HFpEF patients are unable to increase heart rate to compensate for increased output demand (as in the setting of exercise); this is termed chronotropic incompetence. Combined with the characteristic deficit in stroke volume observed in HFpEF patients, many individuals display poor exercise tolerance. Non-simultaneous contraction of the left and right ventricle, dyssychrony, is present in up to 58% of HFpEF patients. However, dyssynchrony is also common in HFrEF and its role in HFpEF in particular remains obscure. While therapies for dyssynchrony,