What Is Cardiac Function?

Cardiac function refers to the mechanical and electrical performance of the heart in its role as a pump, encompassing the processes by which the myocardium contracts and relaxes to circulate blood through the pulmonary and systemic vasculature. It is assessed through measurements of stroke volume, cardiac output, ejection fraction, filling pressures, and myocardial wall motion. The quantitative study of cardiac function draws on fluid mechanics, continuum mechanics, electrophysiology, and biomedical engineering, and is foundational to the design of diagnostic imaging systems and therapeutic devices.

The heart consists of two functional pumps in series: the right ventricle drives deoxygenated blood through the pulmonary circulation, and the left ventricle drives oxygenated blood through the systemic circulation. Normal cardiac output at rest is approximately five liters per minute, achieved through a heart rate of 60 to 80 beats per minute and a stroke volume near 70 milliliters.

Systolic and Diastolic Mechanics

The cardiac cycle is divided into systole, during which the ventricles contract and eject blood, and diastole, during which they relax and fill. Systolic function is characterized primarily by ejection fraction, defined as the fraction of end-diastolic volume ejected per beat; a normal left ventricular ejection fraction exceeds 55 percent. Diastolic function describes the compliance and relaxation properties of the ventricular wall as it fills: impaired relaxation leads to elevated filling pressures and is a major contributor to heart failure with preserved ejection fraction. The NHLBI overview of heart function and the cardiac cycle provides a clinical grounding for these mechanical concepts and their diagnostic relevance.

Electromechanical Coupling

Contraction of cardiomyocytes is initiated by calcium-mediated excitation-contraction coupling. The action potential propagating through the conduction system depolarizes each cell, triggering an influx of calcium through L-type channels and the release of additional calcium from the sarcoplasmic reticulum, which in turn activates the actin-myosin cross-bridge cycle. Synchrony of ventricular activation is essential to efficient pump function: conduction abnormalities such as left bundle branch block create dyssynchronous contraction that reduces ejection fraction. Cardiac resynchronization therapy (CRT) corrects this by pacing both ventricles simultaneously. The biophysical models underlying electromechanical coupling are central to computational cardiac physiology and are reviewed in depth by the Physiome Project resources hosted by IUPS, which support reproducible cardiac modeling.

Assessment and Imaging

Cardiac function is assessed through a range of imaging and functional testing modalities. Transthoracic echocardiography is the most widely used clinical tool; it measures chamber dimensions, wall motion, and Doppler flow velocities to estimate filling and ejection parameters. Cardiac magnetic resonance imaging (CMR) offers superior soft-tissue contrast for quantifying ventricular volumes and myocardial strain without ionizing radiation. Nuclear cardiology techniques, including single-photon emission computed tomography (SPECT) and positron emission tomography (PET), assess myocardial perfusion and metabolism. Invasive hemodynamic assessment using pressure-volume loops obtained from conductance catheters provides the most complete load-independent characterization of ventricular contractility. Research into image-based computational models that integrate these measurements appears widely in IEEE Transactions on Biomedical Engineering.

Applications

The study of cardiac function has applications in a wide range of engineering and clinical fields, including:

• Echocardiography and cardiac MRI system design and algorithm development
• Implantable hemodynamic monitoring for heart failure management
• Cardiac resynchronization therapy device optimization
• Computational modeling of heart mechanics for surgical planning
• Stress testing systems for ischemia detection in cardiology clinics