• Inadequate cellular metabolism secondary to cardiac dysfunction when there is adequate intravascular volume.
• In some cases, the patient already has a disorder that has been previously diagnosed but some factor has caused an acute exacerbation of cardiac function, eg valvular endocardiosis with acute rupture of the chordae tendinae Heart: rupture of chordae tendinae , right atrial or heart base mass that has acutely bled causing pericardial tamponade or left atrial rupture.
• In other cases, clinical condition may have not been previously diagnosed and clinical signs may be slow and gradual in onset, ie cough associated with left atrial enlargement, gradual decrease in exercise tolerance associated with dilative cardiomyopathy Heart: dilated cardiomyopathy (DCM) or dysrhythmias Heart: dysrhythmia , gradual development of cachexia and ascites seen with caval syndrome Caval Syndrome secondary to heartworm disease Cardiopulmonary dirofilariasis.
• Cardiac dysfunction may occur secondary to other, indirectly related diseases such as reduced contractility due to high levels of inflammatory cytokines or dysrhythmias induced by electrolyte abnormalities.
• Heart failure can be classified as:
  • Forward: left ventricular failure secondary to reduced forward flow into the systemic circulation; right ventricular failure secondary to reduced forward flow into the pulmonary circulation.
  • Backward (congestive): secondary to elevated venous pressures, usually secondary to increase in preload and will cause pulmonary edema with left sided failure and tissue bed edema/body cavity fluid accumulation with right sided failure.

Presenting signs

• Typical signs of shock: elevated heart rate, poor pulse quality, prolonged capillary refill time, pale mucous membranes, elevated respiratory rate, cool extremities.
• Exercise intolerance.
• Syncope Syncope or collapse Collapse.
• Mental dullness.
• Plus other clinical signs that can include:
  • Pulse deficits or asynchronous pulses.
  • Cardiac dysrhythmias Heart: dysrhythmia.
  • Jugular vein filling at rest.
  • Peripheral edema.
  • Crackles on thoracic auscultation.
  • Heart murmur Murmur: overview.
  • Tachypnea.
  • Respiratory distress.
  • Muffled heart or lung sounds (due to pleural effusion Pleural: effusion, more typically seen than pulmonary edema in cats).
  • Cyanosis.
  • Ascites.