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In contrast, movement along a single curve represents the operation of the Frank-Starling principle, which indicates that stroke volume, cardiac output, or stroke work varies with preload. The position of a given curve provides a description of ventricular pump performance. A family of the Frank-Starring curves reflects the response of the pump performance of the ventricle to a spectrum of contractile states. 6 In this relationship, the output can be considered to be the stroke volume, cardiac output, or the stroke work. The relationship between the input and output is the ventricular curve or the Frank-Starring relationship (Fig 3). 4,5 The left heart can be analyzed as a pump with an input (the pulmonary venous or mean left atrial pressure) and an output (the cardiac output). Furthermore, cardiomyocyte diam- eter is higher in patients with HF and a normal EF than in those with HF and a reduced EF, but collagen levels may be equally elevated. The clearest difference between the 2 forms of HF is the difference in LV geometry HF with a reduced EF is characterized by eccentric LV hypertrophy, whereas HF with a normal EF is characterized by concentric LV hypertrophy. 3 Heart failure with a reduced and a normal EF has several similarities in LV structural and functional characteristics, including increased LV mass and elevated LV end-diastolic pressure. Table 1 shows the comparison of LV structural and functional characteristics in HF with a reduced and a normal EF. 1,2 Why do patients with HF and a reduced EF and those with HF and a normal EF have marked differences in the EF and the types of left ventricular (LV) remodeling despite similar clinical mani- festations and neurohumoral activation? Consid- ering the similarities and different aspects of the LV structure and function and clinical characteristics between the groups may provide some clues to help answer this question. Furthermore, both groups have substantial neuroendo- crine activation (Figs 1 and 2). Despite the substantial differences in the EF, patients with HF and a reduced EF and those with HF and a normal EF have similar clinical symptoms and signs. failure (HF) has traditionally been divided into HF with a reduced ejection fraction (EF systolic HF) and HF with a normal EF (diastolic HF).