The argument concludes that psychological stress is beneficial for the heart because it elicits the same cardiovascular response as vigorous physical exercise. Therefore, the argument relies on the assumption that the cardiovascular response during an activity is an adequate measure of how beneficial the activity is for the heart. Option (C) correctly captures this assumption and is the correct answer.

Option (A) is irrelevant to the argument, as the argument doesn't claim that exercise can relieve psychological stress.

Option (B) is incorrect because it generalizes the argument's claim beyond the scope of cardiovascular response.

Option (D) may be true but is not necessary for the argument's conclusion.

Option (E) is irrelevant to the argument, as the argument doesn't compare the effectiveness of different methods of maintaining a healthy heart.

Answer: C