Heart failure is a clinical syndrome of congestion and decreased cardiac output. There is activation of the sympathetic nervous system as well as the renin-angiotensin-aldosterone system and vasopressin (ADH) which result in salt and water retention by the kidney and increased thirst (angiotensin II). There is increased volume in the intravascular and interstitial compartments but the circulating blood volume is decreased.
Dyspnea has many possible causes but in case of left heart failure is likely secondary to the combination of elevated left atrial pressure which is transmitted back into pulmonary veins and capillaries with transudation of fluid into pulmonary interstitial and alveolar spaces as well as decreased blood flow to respiratory muscles resulting in increased work of breathing.
Peripheral edema is the result of either high hydrostatic pressure or low oncotic pressure in capillaries. In right heart failure, right heart can pump enough blood to lungs cause in a high right atrial pressure and intravascular fluid overload back to vena cava and causing increased hydrostatic pressure in the capillaries of the legs with transudation of fluid.
Abdominal distension is likely secondary to ascites because of transudation of fluid into the peritoneal cavity in the setting of elevated inferior vena cava pressure in right heart failure as explained above.
NOTE: LEFT HEART FAILURE LEAD TO RIGHT HEART FAILURE
Ascites, liver congestion, increased jugular venous pressure are due to right heart failure.
Pulmonary edema is due to the left heart failure