In order to become fit aerobically it is necessary to get the heart and breathing rates up from normal. It is ok to be a little out of breath when training the heart and lungs. In fact it is a must. The ideal level however, which is not too hard nor too easy, is a level such that, if you were talking you would need to take a breath between every 3 words or so. If you can carry on a normal conversation without difficulty, you probably are not working hard enough. If you can’t talk and are gasping for breath, you are working too hard. Athletes definitely spend time training in that difficult zone but it is not necessary. Certainly be aware that if you are relatively new to exercising this way it won’t be easy at first but it will get easier with practice. Once you have trained aerobically regularly for a many months go ahead and challenge yourself by bumping up the intensity of you like.
Of course the single best thing you can do for your heart health is to be a non-smoker. Not easy I’m sure. Can’t seem to do that? Try consuming only heart healthy foods. So less red meat. Leaner cuts when you do choose it. More fruit and vegetables. Avoid high fat foods such as ribs, bacon, creamy sauces and dressings. Keep sugar intake minimal as well. Excess sugar in the diet, from any source can lead to diabetes which also causes heart disease. Consume a well balanced diet that contains some , but not too much, protein carbohydrates and fat. Yes you need some fat and some carbohydrate in your diet. Carbs are fruit and veggies as well as bread, pasta and sweets. Of course you need more of the fruit and veggie type than the sweet type but whole grain breads, especially dark varieties such as rye or pumpernickel are good too.