Complex sentence: The other 30 to 40% of people develop further symptoms 10 to 30 years after the initial infection, including enlargement of the ventricles of the heart in 20 to 30%, leading to heart failure.
Split into simpler sentences: The other 30 to 40% of people develop further symptoms 10 to 30 years after the initial infection. This includes enlargement of the ventricles of the heart in 20 to 30% leading to heart failure.