Cass,
Had to read your post a couple of times since you say your husband just got his first script for BP meds. But atenolol IS a BP med...I presume it was prescribed after his heart attack, beta blockade being pretty standard treatment in order to improve survival.
Regarding Micardis plus Lasix, the source I use for drug-drug interactions indicates a "moderate" interaction insofar as loop diuretics, being especially potent, can increase the effects of the Micardis.
However, in your husband's case, this may not be such a bad thing if you want his systolic to come down lower than 140-150.
zuzu xx