Cozaar or losartan is ARB, that's right, it is more preferred than ACE inhibitors since it does not cause side effect particularly cough. I am taking cozaar too ;D another is maybe you become tachycardic because as we urinate (which is because sodium excretion is promoted by cozaar), blood volume decreases, as a result , increase in HR occur to compensate in low blood volume by trying to pump more blood. that's the reason i think behind the tachycardia thing.