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.
FIRST RESPONSEâ¢ is >99% accurate from the day of the expected period â in laboratory studies. However, some pregnant women may not have detectable amounts of pregnancy hormone in their urine on the day of the test or may have miscalculated the first day of their period.