On last saturday my wife had gone through a usg when she was exactly 7 weeks and 3 days of pregnancy. but doctors did not get the heartbeat..is it ok?

Probably not: Should be able to see a htbeat at 7 wks 3 days , most likely non viable pregnancy, i would repeat us in 1 week to confirm or refute if no ht beat in one week then something needs to be done remove the products of conception and her doctors should have told her and you what was going on and what the plan should be !

Size matters: This really depends on if this was a transabdominal or transvaginal ultrasound as the latter is more accurate. At this stage in pregnancy, a millimeter or 2 can make a big difference in dating. A heartbeat should be detected when the fetus reaches 10mm in size.

Cardiac Activity: Embyronic cardiac activity must be identified with a crown-rump (embryonic pole) length ≥ 7 mm based on new more stringent guidelines (previously > 5 mm). A 7 mm or greater embryonic pole without cardiac activity is considered a failed pregnancy. I recommend following up with you OB doctor with the results of your ultrasound.

Be patient: In the absence of bleeding a followup us is advised. Often the heartbeat will be seen on followup.