I have never smoked any weed that slowed my heart rate. I'm pretty sure this has never been proven to be an effect of THC. "quote" One of the most consistent effects of cannabis intoxication is an increased heart rate. For this reason alone it would not be normally recommended for patients with cardiovascular problems. However, THC also acts as a smooth-muscle relaxant, relaxing the walls of the arteries, which can result in lower blood pressure and increased blood flow to the tissues[ii][iii]. The effect taken together is analogous to a car changing down a gear. i] Nahas G, Trouve R (1985) Effects and interactions of natural cannabinoids on the isolated heart. Proc Soc Exp Biol Med 180(2):312-6 [ii] Malit LA, Johnstone RE, Bourke DI, Kulp RA, Klein V, Smith TC (1975) Intravenous delta9-Tetrahydrocannabinol: Effects of ventilatory control and cardiovascular dynamics. Anesthesiology 42(6):666-73 [iii] Johnstone RE, Lief PL, Kulp RA, Smith TC (1975) Combination of delta9-tetrahydrocannabinol with oxymorphone or pentobarbital: Effects on ventilatory control and cardiovascular dynamics. Anesthesiology 42(6):674-84