Nitroglycerin does increase heart rate in most people, but not because it stimulates the heart directly. The rise in heart rate is a reflex response: nitroglycerin relaxes blood vessels and lowers blood pressure, and the body compensates by speeding up the heartbeat. This effect, called reflex tachycardia, is one of the most well-documented responses to the drug.
Why Nitroglycerin Raises Heart Rate
Nitroglycerin is a vasodilator, meaning it widens blood vessels. When blood vessels relax and expand, blood pressure drops. Your body has built-in pressure sensors (baroreceptors) in the arteries near the heart and neck that detect this drop almost immediately. In response, your nervous system signals the heart to beat faster to maintain adequate blood flow to your organs.
In research on intravenous nitroglycerin, heart rate increases of up to 100 beats per minute above baseline were observed after blood pressure fell by about 26 mmHg. That’s a dramatic example from controlled animal studies, but it illustrates the relationship clearly: the bigger the blood pressure drop, the stronger the reflex heart rate increase. When researchers blocked the nervous system pathways responsible for this reflex, the heart rate increase was largely prevented, confirming that the heart itself isn’t being stimulated. It’s the body’s automatic correction for lower blood pressure.
How Quickly It Happens
Sublingual nitroglycerin, the tablet or spray placed under the tongue, begins working within 2 to 5 minutes. Blood vessels start dilating almost immediately, and the heart rate response follows closely. In studies measuring artery dilation, the peak effect occurred at about 3 minutes for both tablets and sprays. The spray tends to reach significant dilation slightly faster (around 2 minutes) and sustains it longer, up to about 15 minutes, compared to roughly 10 minutes for the tablet.
Because the drug wears off quickly, the heart rate increase is also short-lived with sublingual forms. Longer-acting formulations like patches or sustained-release capsules produce a more gradual, less pronounced effect on both blood pressure and heart rate.
How Common Is This Side Effect?
The FDA prescribing information for sublingual nitroglycerin lists palpitations (the sensation of a fast or pounding heartbeat) as an occasional side effect. It’s less common than headache, which is the most frequent complaint, occurring in more than 2% of patients. Dizziness and lightheadedness from the blood pressure drop are also more frequently reported than a noticeably faster pulse.
That said, the heart rate increase happens physiologically in most people who take nitroglycerin. Whether you actually feel it depends on how large the increase is and how sensitive you are to changes in your heartbeat. A small bump of 5 to 10 beats per minute often goes unnoticed, while a larger jump can feel like your heart is racing.
When the Heart Rate Response Becomes a Problem
For most people using nitroglycerin as prescribed for chest pain (angina), the mild increase in heart rate is harmless and temporary. But there are situations where the reflex tachycardia can cause trouble.
A faster heart rate means the heart muscle needs more oxygen. In someone having a heart attack or living with severe coronary artery disease, that increased demand can worsen the very problem nitroglycerin is meant to treat. This is one reason nitroglycerin is not recommended when heart rate is already above 100 beats per minute in the absence of heart failure. It’s also avoided when blood pressure is already low (systolic below 90 mmHg), because the further drop could trigger a dangerously large compensatory heart rate spike.
Right ventricular heart attacks deserve special mention. Guidelines from the American Heart Association and European Society of Cardiology have traditionally warned against nitroglycerin in these cases, because the drug reduces the volume of blood returning to the heart (preload). When the right side of the heart is already struggling to pump effectively, that reduction could cause a sharp drop in blood output. A meta-analysis of available studies found the actual risk may be smaller than feared, with roughly 3 additional adverse events per 100 treatments compared to other types of heart attacks, and no deaths directly attributed to nitroglycerin. Still, caution in this setting remains standard practice.
The PDE5 Inhibitor Danger
The heart rate response to nitroglycerin becomes especially dangerous when combined with medications for erectile dysfunction like sildenafil (Viagra), tadalafil (Cialis), or vardenafil (Levitra). These drugs also dilate blood vessels. Taken together, the combined effect can cause blood pressure to plummet, with drops of more than 45% documented in research. In one study, mean blood pressure fell from about 100 mmHg to just 54 mmHg when nitroglycerin was given after sildenafil.
The body responds to this severe drop with a large compensatory heart rate increase. In the same research, heart rate climbed from 131 to 156 beats per minute. But even with the heart beating that fast, it can’t fully compensate for such a dramatic loss of blood pressure. The result can be fainting, dangerously low blood flow to the heart, or in severe cases, cardiovascular collapse. This combination is strictly contraindicated, and you should not take nitroglycerin within 24 to 48 hours of using any PDE5 inhibitor.
What About Long-Term Use?
People who use nitroglycerin regularly, such as through daily patches or long-acting oral forms, often develop some tolerance to both the blood pressure-lowering and heart rate-raising effects over time. The body adjusts, and the reflex tachycardia becomes less pronounced. This is part of a broader phenomenon called nitrate tolerance, where the drug gradually becomes less effective with continuous use. It’s one reason doctors often recommend a “nitrate-free” window of 10 to 12 hours each day, typically overnight, to preserve the drug’s effectiveness.
During exercise, the heart rate picture looks different. A study in adults with heart failure found that sublingual nitroglycerin lowered the pressures in the heart’s filling chambers during exercise but did not significantly change heart rate, stroke volume, or overall cardiac output compared to placebo. This suggests that during physical activity, when the heart rate is already elevated by exercise, nitroglycerin’s reflex effect on heart rate is less noticeable or meaningful.