Thermal preconditioning to simulate shipping, handling and storage conditions did not affect distal tip stiffness values for permanently implantable cardiac leads used for pacing and defibrillation. Leads that were subjected to extreme temperatures and temperature cycling did not show changes in buckle force values compared with control specimens which were maintained at ambient room conditions. Absolute differences between all measurements were small, generally under 0.05 N and were attributable to measurement variability. Buckle force values are used to assess the propensity of leads to perforate the heart, a rare but potentially serious complication of implantable pacing and defibrillation systems. Since preconditioning and buckle force measurement methods have not yet been standardized and no published studies exist, it was unknown whether and how much thermal preconditioning could affect lead buckle force. This study involved eight lead models from all four major lead manufacturers and included both pacing and defibrillation leads spanning a range of materials and construction methods. The preconditioning parameters used in the study, such as temperatures and cycle times, were derived from current industry methods. Knowing whether thermal preconditioning is critical to perforation propensity allows lead manufacturers and regulators to more efficiently direct resources towards ensuring reliability as well innovation. The results of this study can also inform the AAMI working group which is developing industry standards for transvenous pacing and defibrillation leads.