Provide a detailed explanation of the benefits of regular physical exercise for cardiovascular health, focusing on how exercise strengthens the heart and improves blood flow. Your response should contain at least 3 paragraphs. Paragraphs are separated with the markdown divider: ***. Highlight at least 2 sections in your answer with markdown, i.e. *highlighted section*. Include keywords *stronger heart muscle* and *improved circulation* in the response. At the end of your response, please explicitly add a postscript starting with *P.S.*.
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