Heart failure with reduced ejection fraction (HFrEF, EF ≤40%) involves impaired systolic contractile function — the ventricle cannot eject blood effectively. The primary mechanism is loss of functional myocardium (MI, dilated cardiomyopathy) or sustained volume/pressure overload leading to eccentric remodeling (chamber dilation, wall thinning, spherical transformation). Increased wall stress (LaPlace law: wall stress = pressure × radius / 2 × wall thickness) stimulates maladaptive neurohormonal activation (RAAS, SNS, natriuretic peptides). The Frank-Starling curve shifts downward and rightward — higher filling pressures fail to generate adequate stroke volume. Heart failure with preserved ejection fraction (HFpEF, EF ≥50%) involves impaired diastolic relaxation and filling with preserved systolic function. The ventricle is stiff and noncompliant (concentric hypertrophy, myocardial fibrosis, titin abnormalities), requiring elevated filling pressures to achieve normal filling volumes. This elevated left atrial pressure transmits backward to the pulmonary vasculature, causing exercise-induced pulmonary congestion. HFpEF is predominantly a disease of older women with hypertension, obesity, diabetes, and atrial fibrillation. The E/e' ratio on tissue Doppler echocardiography >14 suggests elevated LV filling pressures. Heart failure with mildly reduced EF (HFmrEF, EF 41-49%) is...