Of course, this is a question best suited for your parents’ doctor(s). That being said, my father-in-law who has also suffered a heart attack and is on blood pressure and cholesterol meds, uses his tub regularly. Short sessions of no more than 10 mins and a temp of 100 Deg F are suggested for those who are uncertain how they might respond. But, each person’s health is unique, and depending on a number of things, hot tubs can be dangerous for certain health conditions. Doctors know best and should be advised.