Before we get into the answer, it’s helpful to remember that your heart is actually a muscle, and like any other muscle, it responds to the demands of hard work by getting stronger and larger. So while an enlarged heart – known clinically as cardiac hypertrophy – might not sound good, it can actually be great for your long term heart health.
Let’s break down the anatomy and physiology:
The heart has four chambers, and the size of these chambers determines how much blood the heart can pump with each beat (volume). The thickness of the chamber walls determines how forcefully the heart can beat, or to think of it another way, how fast the blood is moving when it is pumped from the heart. The elasticity of healthy blood vessels helps accommodate changes in heart beat volume and blood speed, allowing the whole system to work efficiently with minimal health risk.
Regular cardiovascular exercise stimulates changes in both the chamber size and the wall thickness of the heart, as the working muscles will need more oxygen and nutrients to continue exercise and the heart will beat faster to accommodate. This stress can be good for your health, as over time, these changes allow the heart to pump more efficiently, using fewer beats to move the same amount of blood.
High blood pressure can also cause heart enlargement, however in this situation only a thickening of the walls occurs. This is primarily seen in the left ventricle, the last chamber of the heart before the blood is pumped into the vessels. This specific enlargement is called left ventricular hypertrophy, and is actually stimulated by a loss of elasticity in the blood vessels. Stiffer blood vessels require the heart to pump harder to move the blood, as there is more resistance from the blood vessel walls that prevents the blood from flowing as easily. Because the overall needs of the body don’t change, the volume of blood pumped per beat will remain the same and no change in chamber size will occur. Overall, thicker walls without a concurrent change in chamber size will complicate good heart function, as the heart chambers may not fill as well and the volume of each heart beat will be decreased.
If you have might blood pressure, it’s worth talking to your doctor about your risk of left ventricular hypertrophy, as it has been associated with sudden cardiac death. If you already have this condition, it’s really worth talking to your doctor because there is evidence that exercise and changes to your diet and body composition can have a positive impact on the heart structure, and you want to be able to make these changes safely.
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Pluim, B. M., Zwinderman, A. H., Laarse, A. V., & Wall, E. E. (2000). The Athlete’s Heart : A Meta-Analysis of Cardiac Structure and Function. Circ, 101(3), 336-344. doi:10.1161/01.cir.101.3.336
Smith, D. L., & Fernhall, B. (2011). Advanced cardiovascular exercise physiology. Champaign, IL: Human Kinetics.