At what rate should my heart be at while i am doing a cardiovascular workout ? if it's too high what should i do to lower it ?

Depends how: Hard you are working out...Increased fitness will result in lower heart rate for given level of exertion.

220 - Age = Max HR: Your maximum heart rate can be calculated as 220 minus your age. For a 34 year old male your max would be 186 beats per minute. Your heart rate should be between 50 and 80% of your maximum heart rate for adequate exercise. This translates to 93 - 148 beats per minute. To lower your heart rate, you should stop exercising immediately, seek medical help if not improving.