The present study examined how cardiovascular and salivary cortisol responses varied in response to an acute challenge in medical students under exam stress versus those not under exam stress. One hundred and twenty-nine medical students were randomly assigned to undertake a CO 2 inhalation test either prior to an examination period (exam group) or during a regular academic period (non-exam group). Heart rate (HR) and blood pressure (BP) were measured for 5min before and 5min after the task, and salivary cortisol samples were collected 1min before and 10 and 30min after the CO 2 inhalation test. Participants also completed a questionnaire measuring self-reported perceived stress.The exam group exhibited significantly higher HR reactivity following the CO 2 inhalation test and slower systolic blood pressure (SBP) recovery compared with the non-exam group. The exam group also reported higher perceived stress and higher stress scores were related to higher HR reactivity following CO 2 inhalation. Female students across both groups exhibited significantly lower SBP reactivity compared with male students. Salivary cortisol levels were consistently lower in the exam group.These findings indicate that ongoing natural stress alters cortisol secretion and cardiovascular responses in the face of an acute stress challenge.