Final answer:
Cardiomegaly is caused by the enlargement of the heart due to chronic strain from conditions like hypertension and coronary artery disease, where narrowed arteries from atherosclerosis make the heart work harder, potentially leading to serious complications.
Step-by-step explanation:
Cardiomegaly, or the enlargement of the heart, is typically caused by chronic strain against vascular peripheral resistance, often seen in conditions such as hypertension and coronary artery disease. With the progression of coronary artery disease, atherosclerosis narrows the coronary arteries, leading to a reduced capacity of these vessels to supply the heart with oxygen-rich blood. This low oxygen condition, called ischemia, alongside the increased effort needed to pump blood against the elevated resistance, can contribute to the enlargement of the heart muscle itself, in an attempt to compensate for the increased workload. When the heart works harder due to high blood pressure or obstructed arteries, it may grow larger in response to the increased demand but over time, this enlargement can lead to further cardiac complications including arrhythmias, heart failure, or cardiac arrest.