At 48, he seemed to have everything going for him, at least as far as his health was concerned. He was physically fit, a regular marathon runner and someone who took his fitness seriously. He had no chest pain, no breathlessness and no reason to suspect that anything could be wrong with his heart. But there was one detail that he had overlooked: family history. So, when his brother underwent angioplasty at the age of 52 and spoke of male predecessors in the family having a shorter lifespan, he decided to look more closely at his own risk.Although he felt perfectly healthy, he decided to undergo a CT coronary angiogram to check the condition of his heart arteries. What the scan revealed was nothing short of shocking. He had blockages ranging from 75 to 90 per cent in all four major coronary arteries. His condition was so extensive that he needed bypass surgery rather than angioplasty. Bypass surgery is generally recommended when the blockages are too extensive or complex to be treated effectively with stents.Imagine running marathons, pushing your body to its limits and believing that you are at the peak of fitness, only to discover that your heart’s blood supply is severely compromised. This is precisely why one should never confuse physical fitness with freedom from heart disease. The case also raises an uncomfortable but important question: How can someone with such severe heart blockages remain completely symptom-free?The heart has a remarkable reserve capacityTo understand this, one must first appreciate just how extraordinary the human heart is. The heart is not an ordinary pump. It has an enormous reserve capacity and can dramatically increase the amount of blood it pumps when the body needs it. At normal rhythms, most people require approximately five litres of blood per minute to meet the body’s needs. During intense physical activity, however, the heart can increase its output several times over, potentially reaching 35 to 45 litres per minute in highly trained individuals.This remarkable reserve can sometimes mask the effects of narrowing in the coronary arteries.Think of it this way: a road may have several bylanes blocked but traffic might still move when the number of vehicles is low. The problem becomes apparent when traffic increases and the road can no longer cope with the demand. Similarly, a person may feel perfectly normal during everyday activities because the heart is still managing to supply enough blood. Even during exercise, the heart’s considerable reserve may initially help compensate for reduced blood flow.However, this does not mean the blockages are harmless. When the heart’s demand for oxygen-rich blood exceeds what the narrowed arteries can deliver, the consequences can be serious.Story continues below this adWhen the body gets used to doing lessAnother reason symptoms may go unnoticed is gradual deconditioning. Sometimes, people unconsciously reduce their physical activity as their capacity declines. They may take the stairs less often, walk more slowly or avoid activities that leave them tired.What they describe as getting older, feeling a little less energetic or simply being out of shape could, in some cases, be the body’s way of signalling an underlying cardiac problem. The symptoms are not necessarily absent; they may simply be so subtle that they are dismissed or overlooked.The danger of silent ischaemiaThere is another particularly concerning phenomenon known as silent ischaemia. This occurs when the heart muscle does not receive enough oxygen-rich blood, usually because of narrowed coronary arteries. Normally, reduced blood supply may cause chest discomfort or pain. However, some people experience no obvious warning signs at all. This is particularly important in people with diabetes. Diabetes can damage the nerves responsible for transmitting pain signals, meaning that a person may have significant cardiac ischaemia without experiencing the typical chest pain.Don’t wait for your heart to complain.The lesson from this 48-year-old marathon runner’s experience is not that exercise is dangerous or that every fitness enthusiast should be worried. Regular physical activity remains one of the most important ways to protect cardiovascular health. But fitness alone cannot rule out coronary artery disease.Story continues below this adSo, track your family history for chronic illnesses, do not ignore the routine blood pressure, cholesterol, blood sugar checks. Do not dismiss unusual fatigue, reduced exercise capacity, breathlessness, unexplained sweating or discomfort during exertion. Even mild or unusual symptoms deserve medical evaluation.There is no single test that is necessary for everyone. Depending on age, family history, symptoms and other risk factors, a cardiologist may recommend further evaluation. This could include a coronary artery calcium score, an exercise stress test or a CT coronary angiogram. Importantly, CT coronary angiography is not a routine screening test for every healthy person. The decision should be individualised after discussion with a doctor.The absence of symptoms is not proof of the absence of heart disease. So, keep running, keep exercising and keep yourself fit. But don’t let your fitness levels become a reason to overlook your heart health.(The author is lead cardiologist and medical director, Sparsh Hospital, Bengaluru)