Imagine judging the efficiency of a car solely by how fast it can travel. Two cars might reach the same speed, yet one consumes twice as much fuel to get there. Looking only at speed would overlook a crucial aspect of performance.

The heart works in much the same way. It is not enough to know how much work it performs. Equally important is understanding how much energy it consumes while doing that work. This hidden relationship between effort and energy has fascinated physiologists for decades and is now emerging as one of the most promising frontiers in cardiovascular medicine. Researchers including Prof. Lawrence Mulligan of Cooper University Hospital are helping to bring these concepts closer to everyday clinical practice, offering fresh ways to understand heart disease before it becomes obvious through traditional tests.

At its core lies the following question: how efficiently does the heart convert oxygen into useful work? Every heartbeat has a price and like every muscle in the body, the heart needs energy to contract. Unlike the muscles in your arms or legs, however, it never gets a day off. Even while you sleep, your heart continues its relentless work, supplying oxygen and nutrients to every tissue in your body.

That constant activity demands an enormous supply of energy. Heart muscle cells are packed with mitochondria, the tiny structures often described as the power stations of the cell. In fact, heart cells contain more mitochondria than almost any other cell type in the human body, dedicating roughly one third of their internal space to energy production.

These microscopic power plants generate the fuel needed for every contraction by consuming oxygen and breaking down nutrients such as fats and carbohydrates. A healthy heart manages this energy supply and results in an efficiency ratio of 30-35%.

The heart is remarkably adaptable. It can switch between different fuel sources depending on the body’s needs. During exercise, pregnancy, or periods of limited oxygen availability, it adjusts its metabolism to continue functioning efficiently. This flexibility helps explain why healthy hearts can cope with extraordinary physical demands while maintaining reliable performance.

Problems arise when the physical demands, ie myocardial work, change without a parallel increase in oxygen delivery. A diseased heart may still pump blood, but it often has to consume considerably more oxygen to perform the same amount of work, leading to a decrease in myocardial efficiency. In effect, the engine begins burning more fuel while producing less useful output. Long before obvious symptoms develop, subtle changes in energy use may already be signalling that something is wrong.

Understanding this hidden economy requires scientists to think about the heart in a slightly different way. Traditionally, cardiologists have focused on measuring blood flow, chamber size, blood pressure, or the strength of contraction. These remain essential clinical tools, but researchers have increasingly recognised that they do not fully capture how well the heart is functioning.

Instead, they have begun asking how much oxygen the heart consumes for every unit of useful work it performs. This concept is known as myocardial efficiency. In simple terms, myocardial efficiency compares the useful work performed by the heart with the oxygen required to achieve it. A normal and efficient heart performs substantial work with the necessary oxygen, resulting in the 30-35% metric. A less efficient heart burns much more oxygen to accomplish the same task.

Closely related is another measure known as mechanical efficiency. Although the names sound similar, they describe different aspects of cardiac performance. Mechanical efficiency focuses on how effectively the heart converts its total mechanical energy into useful pumping work. Myocardial efficiency looks instead at the relationship between useful work and oxygen consumption, making it a more direct reflection of the heart’s metabolic health.

For many years these measurements remained largely confined to research laboratories. The reason was simple. Obtaining them required invasive procedures involving specialised catheters inserted into the heart to record pressure and volume changes throughout each heartbeat. These procedures provided remarkable scientific insights but were too complex and impractical for routine clinical use.

Fortunately, technology has changed the landscape. Modern imaging techniques, such as positron emission tomography, combined with advanced echocardiography, now allow researchers to estimate many of these values without entering the heart itself. This shift has reignited interest in myocardial efficiency as a potentially valuable clinical tool.

Even more exciting are efforts to develop simpler methods that rely on readily available measurements such as blood pressure, heart rate and ultrasound imaging. If successful, these approaches could eventually allow physicians to monitor cardiac efficiency much more easily and more frequently, such as at regularly scheduled visits.

One reason myocardial efficiency has attracted growing attention is that it often reveals changes that conventional measurements overlook. Two people may have similar blood pressure, similar heart rates and similar pumping capacity. On the surface, both hearts appear healthy. Yet one heart may already be working considerably harder than the other, consuming much more oxygen for the same result.

That hidden inefficiency may represent the earliest stages of cardiovascular disease. Researchers have found evidence that myocardial efficiency changes across a wide range of conditions, from hypertension and heart failure to obesity, diabetes and aortic valve disease. In many cases these changes occur before more familiar signs of disease become obvious.

This opens an intriguing possibility. Rather than waiting until damage becomes visible through declining pumping function or worsening symptoms, doctors might someday detect disease much earlier by monitoring how economically the heart performs its work.

Such an approach mirrors developments in many other areas of medicine. Modern healthcare increasingly aims to identify subtle physiological changes before irreversible damage occurs, allowing treatment to begin earlier when interventions are often most effective.

Interestingly, reduced efficiency is not an inevitable consequence of increased workload. Consider endurance athletes. Years of sustained aerobic training transform the heart. Its chambers enlarge, its walls remodel and its ability to pump blood increases dramatically. To an untrained observer, some of these structural changes might even resemble those seen in heart disease.

Yet the athlete’s heart remains remarkably efficient. Long term endurance training increases the heart’s ability to deliver oxygen while improving many aspects of cellular metabolism. Blood vessels become more numerous, oxygen delivery improves and the heart learns to generate greater output with relatively modest increases in energy demand. The result is an engine that has become both larger and more capable without becoming wasteful.

Pregnancy provides another striking example. During pregnancy, a woman’s heart faces one of the greatest natural physiological challenges encountered in adult life. Blood volume rises substantially, cardiac output increases by as much as half and the heart enlarges to accommodate these demands.

Despite this enormous increase in workload, research suggests that myocardial efficiency remains largely preserved throughout normal pregnancy. Although the heart works harder, it continues to use its available energy remarkably well.

These examples demonstrate that increased workload alone does not necessarily reduce efficiency. Healthy hearts possess an extraordinary capacity to remodel themselves while maintaining a careful balance between energy consumption and useful work.

The real challenge begins when disease disrupts those finely tuned adaptations. Disease begins to alter that balance in ways that are often invisible at first. Heart failure provides one of the clearest examples. As the heart weakens, it frequently consumes increasing amounts of oxygen while producing less effective pumping. In other words, the engine becomes progressively less economical or efficient. Studies have shown that lower myocardial efficiency is associated with poorer outcomes, suggesting that measuring efficiency may help identify patients at greater risk before traditional indicators fully capture the severity of their condition.

Hypertension tells a similar story. High blood pressure forces the heart to pump against greater resistance, increasing its workload and oxygen requirement. Initially, the heart adapts by thickening its muscular walls, but this adaptation comes at a cost. Over time, efficiency declines, coronary blood flow can become compromised and the risk of heart failure rises. Measuring myocardial efficiency may therefore offer a way to detect these changes while they are still potentially reversible.

Metabolic disorders such as obesity and diabetes also influence the heart’s energetic balance. These conditions alter how heart muscle uses fuel, affecting its remarkable metabolic flexibility. Instead of seamlessly switching between different energy sources, the heart becomes less adaptable and gradually less efficient. This growing recognition that metabolism lies at the centre of many cardiovascular diseases has encouraged researchers to look beyond simple measures of pumping performance and towards the underlying processes that power every heartbeat.

Ageing itself also contributes. As we grow older, the body’s largest artery, the aorta, gradually becomes stiffer. This seemingly modest change has important consequences. A less compliant aorta forces the heart to generate higher pressures with every beat, increasing both the work performed and the oxygen required to perform it. The heart may continue functioning normally for years, but it is doing so at an increasing energetic cost.

To better understand these relationships, Prof. Lawrence Mulligan and colleagues have turned to sophisticated computer modelling. Rather than relying solely on difficult or invasive experiments, they developed detailed simulations of the human cardiovascular system that recreate the interactions between the heart and blood vessels under different physiological conditions.

These virtual models allow researchers to explore questions that would be difficult, expensive or impractical to answer in people. By simulating healthy arteries, progressively stiffer blood vessels and different heart rates, they can examine how changes in the cardiovascular system influence myocardial efficiency. Their findings reinforce what clinical observations have suggested for many years. As arteries stiffen or heart rate rises excessively, the heart becomes progressively less efficient, requiring more oxygen to perform its essential work.

Perhaps most importantly, this work points towards simpler methods of estimating myocardial efficiency using measurements already familiar in everyday clinical practice, including blood pressure, heart rate and standard cardiac imaging. If these approaches continue to prove reliable, they could make routine assessment of cardiac energetics practical for far larger numbers of patients than is currently possible.

That possibility reflects a broader shift in medicine. Increasingly, healthcare is moving away from simply identifying established disease and towards detecting subtle changes in physiology before permanent damage occurs. Rather than waiting for the heart to fail, clinicians may eventually be able to recognise that it is beginning to work less efficiently and intervene earlier.

The heart has often been described as a pump, but perhaps it is more accurate to think of it as an extraordinarily sophisticated energy management system. Every beat represents a careful negotiation between oxygen supply, metabolic demand and mechanical performance. When that balance is preserved, the heart can sustain a lifetime of work with astonishing reliability. When it begins to drift, even before symptoms appear, important clues about future cardiovascular health may already be present.

By revealing this hidden economy, research into myocardial efficiency offers a richer understanding of how the heart functions in both health and disease. As Prof. Lawrence Mulligan and fellow researchers continue refining these concepts and developing practical ways to measure them, they are opening the door to a future in which clinicians may detect cardiovascular problems earlier, tailor treatments more precisely and help more people maintain healthy hearts for longer.