85y male, low bp 80/50 past week, sudden presyncope, rhr 39, bp 140/86. no chest discomfort. history of triple bypass. is it likely to be a heart attack?

Go to hospital now: I'm assuming "additional patient information" refers to you, not 85yo male referenced in question. Elder pts w/low BP should be evaluated immediately especially if feel like about to pass out. While heart attacks can be silent, that's beside the point. If this 85yo has many illnesses & "do not resuscitate" order, then just keep comfortable. But if he wants everything done, don't ignore such low hr.

Possible: Need exam and ekg etc. May be overmedicated or off cycle from high to low. Fluid shifts, dehydration can also relate. The pulse of 39 may be a transient heart electrical block and needs holter monitor to discern- could need pacemaker.