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 Some pregnant women do not mount a tachycardia, or can even produce a bradycardia. This can be paradoxical, due to vagal stimulation [see above] or if the woman is taking beta‐blocker medication

 Women with pacemakers have a fixed upper heart rate

 Athletes may have a very slow baseline heart rate

 Haemoglobin concentration is a useful measure of blood loss, only after there has been fluid resuscitation

During the acute phases of loss, the haemoglobin concentration will not change. Rapid movement of fluid from the extracellular to the intravascular compartment and intravenous clear fluids, will result in a fall in haematocrit. A falling haematocrit may be the only indicator of a slow steady bleed. A rapidly falling haematocrit associated with early signs of hypovolaemia is suggestive of severe loss.