Along with its needed effects, valacyclovir (the active ingredient contained in Valtrex) may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention. The increased heart rate persists after several months (estimate my resting heart rate has gone up 10-15 beats per minute. On the other hand, I've become increasingly sedentary lately, with decreased fitness, so that may contribute to increased resting heart rate. Also,and this is something that I found out in the last year by finding the bottle of valtrex hidden in her trunk,she has herpes. She also has a heart condition called tachacardia where her heart beats about 3 times as fast as a normal person. When you have heart failure, your heart tries to compensate for its lack of pumping power by beating faster (tachycardia) to keep up the same flow of blood around your body. Summary. Heart rate increased is found among people who take Valtrex, especially for people who are female, 60+ old , have been taking the drug for 1 month, also take medication Folic Acid, and have Osteoporosis. View detailed reports from patients taking valtrex who experienced heart rate increased. Reports are from official medical reports as well as online extractions from user reviews and forum discussions. Rare Side Effects With Valtrex Rare side effects happen in very few patients taking the drug. Because these side effects are so rare, it is difficult to tell whether they are caused by the Valtrex or by something else. An increased heart rate, also known as tachycardia, is a heart rate that's beyond the normal range for a typical resting heart rate. Resting heart rates are the number of times per minute that your heart beats while you're at rest or sleeping. Tachycardia means an increased heart rate above 90 beats per minute. Tachycardia can be a physiological response to various stimuli such as a symptom of a number of illnesses. If you have an itch on the body, a rash or increased heart rate, stop taking Valtrex. You may be having an allergic reaction to the medication, and your doctor should be informed about this right away.