I don't get any headaches, just a flushed face. My heart rate goes up to about 100-110, because I check it. My resting heart rate is about 60.
I've a three day, two night punting session coming up soon. I'm not sure if I should take 100mg every 24 hours, or 50mg every 12 hours. Either will be safe, as I've taken Viagra for over 3 years on and off.