1 The heart's internal pacemaker regulates and times the beating of the heart via electrical signals.  Electrical signals start at the SA node, causing atria contraction, and then move on to AV node, delaying electrical impulses to allow blood from the atrium to fill the ventricles.
With the First Response new Early Response Twist Pregnancy Test, you can test as early as 6 days before your missed menstrual period. This is the only test that allows you to find out this early, as it is sensitive enough to capture the very scant amounts of the pregnancy hormone.
Find out the earliest day you can take a pregnancy test. Please enter a valid date. Start with the first day of one period and count right up to the day before the first day of your next period. Count the first day of bleeding or spotting as day one. The average cycle length is 28 days, but can range anywhere from 20 to 45 days.