What is different btwn cardio workout and stressful situations where hr goes to 150? both train the heart, but one is healthy and the other is not?

Exercise, stress: stress involves a wide variety of internal physiologic changes that alter the organism internally widely including adverse changes in immune function, inducing endothelial vascular dysfunction etc. Mediated via a variety of hormonal and neurotransmitter mechanisms. Physical exercise for purposes of cardiovascular conditioning does not trigger all of the same mechanisms and is thus preferred