Diana - I think the answer is going to be about a minute for most people. You have about 5 litres of blood in your body (at least most people do) and the average heart pumps about 70 ml of blood out with each beat. The next bit is going to depend on your resting heart rate. I think most people have an average resting heart rate of about 70 beats a minute (somewhere around there). So, if you multiply the amount of blood that the heart can pump by the number of beats in a minute, you actually get about 4.9 litres of blood, which is almost your whole body's worth of blood. So, in a minute, you will pump the entire blood volume around your body.