The human erectile mechanism is an intricate interplay of hormonal, vascular, neurological, sinusoidal, pharmacological, and psychological factors. However, the relative influence of each respective component remains somewhat unclear, and merits further study. We investigated the role of venous outflow in an attempt to isolate the key determinant of erectile function. Dynamic infusion cavernosometry and cavernosography was conducted on 15 defrosted human cadavers, both before and after the systematic removal and ligation of erection-related penile veins. Preoperatively, an infusion rate of more than 28.1 mL/min (from more than 14.0 to 85.0 mL/min) was required to induce a rigid erection (defined as intracavernosal pressure [ICP] exceeding 90 mmHg). Following surgery, we were able to obtain the same result at a rate of 7.3 mL/min (from 3.1 to 13.5 mL/min) across the entire sample. Thus, we witnessed statistically significant postoperative differences (all P ≤ .01), consistently elevated ICP, lower perfusion volumes, and a general reduction in time taken to attain rigidity. The cavernosograms provided further evidence substantiating the critical role played by erection-related veins, whereas histological samples confirmed the postoperative integrity of the corpora cavernosa. Given that our use of cadavers eliminated the influence of hormonal, arterial, neurological, sinusoidal, pharmacological, and psychological factors, we believe that our study demonstrates that the human erection is fundamentally a mechanical event contingent on venous competence.