The cigarette contains harmful substances to the organism, capable of modifying the cardiac autonomic modulation and bringing important damages to the health. This study aimed at calculating the acute effects of smoking on the Heart Rate Variability (HRV) and the HRV of smokers. Thirty-one young smokers aged between 20 and 30 years of both genders were evaluated. Twelve participants were excluded due to overweight/obesity, hypertension, diabetes, respiratory diseases, cardiac and/or neurological diseases. The Fagerstrom Tolerance questionnaire was applied to estimate the degree of nicotine-dependency. We analyzed time domain and HRV frequency indices, recorded in the control group and during smoking. The control group consisted of smoking simulation. At rest, the HRV was reduced in the control group (LF (nu): Controls + 11 vs. 70.8 Experimental: -80.6 + 6; p = 0.03; CI (nu): Control-29.2 + 11 vs. 19.4 + Experimental-6; p = 0.03) and, during the smoking protocol, the HRV was reduced in the experimental group (LF (nu): Control-60.78 + 11 vs. 77.7 + Experimental-8; <0.01; CI (nu): Control-39.3 + 22 Experimental vs 22.3 + -8; p <0.01). Smoking can greatly reduce the HRV.