The cardiovascular system of the trained endurance athlete differs in a number of ways from the untrained person.These include:
1.increased red blood cell mass and blood volume
2.increased numbers of mitochondria and capillaries in leg muscles.
3.lower peripheral arterial resistance
4.lower systolic and diastolic blood pressure during exercise.
Those and likely other factors I have neglected to mention will be found in both the elite and the non endurance athletes. What distinguishes the elite endurance athlete is the capacity of left ventricle to fill with blood quickly without significant increase in the ventricular pressure. The elite have much better diastolic function.While endurance training and high intensity training may somewhat improve diastolic function , they do not seem capable of developing the super compliant left ventricles of the world class endurance athletes.Genetics provide the substrate for the marathon winner,training finishes the process.