<p>This study aimed for the first time to demonstrate the effects of combination of L-citrulline and sildenafil (L-Cit + S) on penile and testicular vascular perfusions in dogs regarding the semen quality and hormonal profile. Normospermic German Shepherd dogs were subdivided into three groups (<i>n</i> = 6/each); control group that injected 1&#xa0;ml saline, second group subjected to L-Citrulline intravenous injection (L-Cit), and third one administrated oral dose of sildenafil with injected L-Cit (L-Cit + S). Dogs were examined at time points of assessment by hours. Semen collection, blood sampling, hormonal assaying, Doppler evaluation and testicular echo-texture analysis were performed. Testicular colored area (TCA) elevated significantly (<i>P</i> = 0.03) in L-Cit group at 8–120&#xa0;h compared to other groups. While volume, echogenicity, and heterogeneity were not changed (<i>P</i> ≥ 0.05) among groups. Testicular and penile arteries Doppler indices were decreased (<i>P</i> = 0.01) in L-Cit group from 1 to 48&#xa0;h with a sharp decrease (<i>P</i> = 0.01) was observed in L-Cit + S group within 1–8&#xa0;h with a significant (<i>P</i> = 0.01) elevation of peak velocity and blood flow rate within the same hours in the same group. Motility % and sperm concentrations were increased (<i>P</i> = 0.02) at 4&#xa0;h in third group. Circulating L-Cit levels were increased in second and third groups from 4 to 24&#xa0;h, while S levels were (<i>P</i> = 0.01) increased from 1 to 4&#xa0;h only in third group. An elevation of nitric oxide and estradiol levels was observed (<i>P</i> = 0.01) form 1&#xa0;h in L-Cit + S group compared to other groups, while testosterone levels were increased (<i>P</i> = 0.01) from 1&#xa0;h but rapidly declined till reach a lowest value at 48&#xa0;h compared to other groups. Addition of L-citrulline to sildenafil demonstrated a more efficiency in improvement of blood flow, hormonal profile, and semen quality than using sildenafil alone due to the action of L-Cit on nitric oxide.</p>