Can a rapid heartbeat be a sign of old drug use?

Yes. Chronic methamphetamine, ecstasy, & Cocaine use can lead to cardiac damage, a sign of which could be tachycardia (rapid heart rate). Chronic lsd, pcp, psilocybin, and mj use in susceptible individuals, can lead to brain thinking distortions that can trigger anxiety that can show up as tachycardia.