I have snorted ~90mg on 600mg of DXM, taken 300 orally on 3 blotters, and snorted 160 on it's own on many occasions.
I can't say that I think you are likely to have a dangerous heart issue from this chemical, who knows though.
Ever been on a mile rune, a fight, adrenaline rush, physical exertion, etc? Your heart can handle it better than ya might think. Getting anxious over your heart beating faster and faster to your perception meshed with psychedelics isn't the first measure of harm reduction I would take, but if you really think something is wrong a second opinion from somebody you know could help?