Repressors -- people who unconsciously inhibit their display of emotion -- exhibit significant increases in heart rate when they encounter emotion-provoking situations  Nonrepressors have similar physiological responses when they encounter such situations and consciously inhibit their display of emotion
Thus the very act of inhibiting displays of emotion, whether done consciously or unconsciously, causes a sharp rise in heart rate
Encountering an emotion-provoking situation is not sufficient to cause nonrepressors' heart rates to rise sharply.