• Renin–angiotensin system
• metabolic syndrome
• hypertension

To the Editor It was with great interest that I read the recent article by Suarez-Barrientos and colleagues.1 However, I think there is one very important aspect that has been left out of this very good clinical investigation and that is blood volume. One of the principal problems of heart pumping is the availability of enough volume of blood for pumping. If there is insufficient volume, then the heart has to alter its rate …