Kissing your boyfriend elevates his heart rate based on a key difference between the two of you. According to Curiosity.com, when men and women kiss, their bodies set off a chain of hormones. Both of their bodies release adrenaline and cortisol, two hormones that respond to stress. However, according to Discovery, their bodies also release oxytocin, an important chemical in bonding, though at different levels. His body releases less oxytocin, leading to a longer fight-or-flight response, and her body releases more, creating a tend-and-befriend response. So your boyfriend is more than likely going to have a racing heart longer than you, simply because he's a male.

Your boyfriend's heartbeat may rise when you kiss him due to how he values physical intimacy. Research in a 2012 issue of "Personality and Social Psychology Bulletin" indicates that men are more likely than women to initiate physical intimacy as a show of love. This difference reveals that men place value in physical acts in a relationship. When you kiss him, you reaffirm this value and prime him for engaging in physically intimate activity. You meet him where he is and show him a form of love he enjoys, exciting him and thus increasing his pulse.

Performance during physical intimacy is important to men, so your boyfriend's heart rate may climb when you kiss him because he's nervous. Kissing is often a cue for sexual activity, which is important to men in relationships. Men face a different pressure than women to have adequate performance during physical intimacy. Your boyfriend wants to prove to you, as well as others, that he can meet your physical needs. This anxiety can stem from negative experiences during physical intimacy or a feeling of inexperience. A simple kiss may spur an anxious reaction, leading to an increased heart rate.

The reason behind your boyfriend's fast-beating heart can simply be you. Kissing does more than release numerous chemicals in your and your boyfriend's brains. It also is a reminder to him that he is with someone special. When you kiss him, you excite his thoughts and feelings about you. His increased heart rate may just be a sign that he loves you and likes to connect with you physically and emotionally, a feat easily accomplished by a kiss.