Causes
The causes of cardiomegaly are not well understood and many cases of cardiomegaly have no known cause. Prevention of cardiomegaly starts with detection. If a person has a family history of cardiomegaly, one should let ones doctor know so that treatments can be implemented to help prevent the worsening of the condition. In addition, prevention includes avoiding certain lifestyle risk factors such as tobacco use and controlling ones high cholesterol, high blood pressure, and diabetes. Non-lifestyle risk factors include a family history of cardiomegaly, coronary artery disease (CAD), congenital heart failure, atherosclerotic disease, valvular heart disease, exposure to cardiac toxins, sleep-disordered breathing (such as sleep apnea), sustained cardiac arrhythmias, abnormal electrocardiograms, and cardiomegaly on chest X-ray. Lifestyle factors that can help prevent cardiomegaly include eating a healthy diet, controlling blood pressure, exercise, medications, and not abusing alcohol and cocaine. Current research and the evidence of previous cases link the following (below) as possible causes of cardiomegaly.The most common known causes of cardiomegaly are congenital (patients are born with the condition based on a genetic inheritance), high blood pressure (which can enlarge the left ventricle causing the heart muscle to weaken over time), and coronary artery disease.
For some people cardiomegaly is a temporary condition, which can resolve on its own, making ones lifestyle normal like before. Others may have a permanent enlargement, which would then need to be taken care of by the above treatment options.Lifestyle changes

Smoking cessation
Limiting alcohol and caffeine intake
Maintaining a healthy weight
Increasing fruits and vegetables in a daily diet
Limiting consumption of high-fat and/or high-sugar foods
Getting adequate restful sleep

References
Further reading
Amin, Hina; Siddiqui, Waqas J. (2019). "Cardiomegaly". StatPearls. StatPearls Publishing. PMID 31194436. Ampanozi, Garyfalia; Krinke, Eileen; Laberke, Patrick; Schweitzer, Wolf; Thali, Michael J.; Ebert, Lars C. (1 September 2018). "Comparing fist size to heart size is not a viable technique to assess cardiomegaly". Cardiovascular Pathology. 36: 1–5. doi:10.1016/j.carpath.2018.04.009. PMID 29859507. S2CID 44086023. Agostoni, PierGiuseppe; Cattadori, Gaia; Guazzi, Marco; Palermo, Pietro; Bussotti, Maurizio; Marenzi, Giancarlo (1 November 2000). "Cardiomegaly as a possible cause of lung dysfunction in patients with heart failure". American Heart Journal. 140 (5): A17–A21. doi:10.1067/mhj.2000.110282. PMID 11054632. Luedde, Mark; Katus, Hugo; Frey, Norbert (1 January 2006). "Novel Molecular Targets in the Treatment of Cardiac Hypertrophy". Recent Patents on Cardiovascular Drug Discovery. 1 (1): 1–20. doi:10.2174/157489006775244290. PMID 18221071. External links

American Heart Association