Tour de France cyclists have big hearts

Tour de France cyclists have big hearts — literally:

Researchers who examined the hearts of former Tour bikers found that the athletes' hearts were from 20 to 40 percent larger than average, said Dr. Francois Carre of the Centre Hospitalier Universitaire de Rennes, France, speaking at a meeting of the European Society of Cardiology.
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Carre found that the athletes' hearts shrank nearly a quarter in size after they finished riding professionally. Still, the cyclists remained in excellent physical condition.

This still leaves some questions: How big were the cyclists hearts before they started training? Did they start with larger hearts, or did they possess hearts that adapted more to training than others'? Or did their hearts grow as a result of performance-enhancing drugs?