Your heart is central to your body's functioning, and your healthy life. Everyone needs to keep their hearts healthy through exercise, but not all exercises are equally good for your heart.
Your cardiovascular system needs steady activity that is strenuous, but not so strenuous that you tire yourself out or hurt yourself. Pushing yourself too hard is equally as bad as not exercising at all.
In order to promote a healthy heart, you'll need to train your heart to be comfortable with prolonged strenuous activity. Productive cardiovascular workouts take about twenty minutes, with time for warm up and cool down.