What Causes Sudden Reduction In Blood Pressure In A Person With Heart Disease?

My husband had acute heart failure on 3/13/15. Since then he has lost 18 lbs. Tonight he had a blood pressure of 84/58. Earlier it was 82/50. Should we be concerned? He sees the cardiologist on Monday. Earlier in the day it had been 96/64. Pulse is always around 73-78.