The metabolic workhorse that never rests. The heart beats two and a half billion times in a lifetime, drawing its energy from a fuel mix that shifts with the body's state.
Four chambers, valves, and a conduction system that fires from the sinus node down — the heart is both pump and its own pacemaker. Cardiomyocytes are packed with mitochondria, the densest mitochondrial content outside brown fat: this is an organ built for continuous aerobic work. It extracts oxygen from coronary blood almost completely at rest, so more work means more flow, not more extraction.
Metabolic Pathways
Fatty acids dominate at rest and in fasting — high ATP yield per carbon, oxygen-hungry.
Glucose and lactate rise after meals and in exercise — the fed heart burns sugar and recycles lactate via the lactate shuttle.
Ketone bodies contribute in fasting and heart failure, where the metabolic profile shifts pathologically.
Regulation
Coronary flow is the metabolic governor: adenosine and metabolic dilators match supply to demand beat by beat.
Catecholamines raise rate and contractility — the epinephrine arm of exercise.
Thyroid hormone sets the basal tempo; thyroxine excess races the heart.
ANP and BNP — its own hormones — signal volume status to the kidney.
Its oxygen supply is the whole of cardiology: atherosclerosis of the coronaries is the world's leading killer.
Clinical Relevance
Myocardial infarction: coronary occlusion with myocyte death — muscle that does not regenerate.
Heart failure is pump-metabolism failure together: the failing heart reverts toward fetal glycolysis.
Cardiac hypertrophy adapts to load until decompensation — the athlete's heart's dark twin.
Endocrine Functions
Content consolidated from the former Heart (Endocrine) page.
Physiological antagonist of vasopressin and aldosterone — the volume system's two philosophies.
With the circulatory system: endocrine sensing built into the pump itself.
BNP drives guideline decisions in dyspnea triage daily.
NT-proBNP: the heart failure biomarker — diagnosis and prognosis in one number.
ARNI drugs potentiate natriuretic peptides by blocking their breakdown — heart failure therapy by design.
Atrial distension pathology — mitral stenosis, heart failure — chronically elevates the hormones, which is why the assay works for diagnosis and tracking alike.
The endocrine heart reframes failure: the pump was measuring volume all along, and its hormones are the measurement you can order on a blood draw.