If bp is under control you can have heart attack or cardiac arrest?

Yes, unfortunately: If you have coronary artery disease, smoke, have high cholesterol, uncontrolled diabetes and many other problems, unfortunately you are still at risk for a heart attack or cardiac arrest, even if your BP is under control.

Absolutely.: There are many noncardiac causes of cardiac arrest. BP control, other risk factor modification definitely improves your health and longevity. The best way to think is shifting a curve - kind of like this image. Even coronary artery disease is possible with excellent BP control, cholesterol and risk modification. But it is less likely.