Abstract Background Subcutaneous implantable cardioverter-defibrillators (SICDs) offer primary and secondary prevention of sudden death without transvenous leads in individuals not requiring pacing therapy. Intermuscular placement of the SICD generator between the latissimus dorsi (LDM) and serratus anterior (SAM) muscles is often recommended. This specific technique results in reduced defibrillation impedance and subsequently optimal defibrillation thresholds, reduced risk of pocket complications and infections, reduced device migration, and enhanced patient comfort and cosmetic outcomes. Despite the recommendation for an intermuscular implant technique utilizing a mid-axillary incision line, there is limited research describing this anatomical space to avoid complications. In this anatomic study, we examined this anatomical space. Our aim was to provide a better understanding of the interplay between the involved muscles and a proper location of an incision line. We also defined the location of the long thoracic nerve (LTN) relative to this space, which if transected, would lead to a winged scapula. Methods We examined 18 cadavers; 12 (66.7%) were female donors and 6 (33.3%) were males. We measured the distance from the anterior border of the LDM in relation to the cadaver back (A) and in relation to the anterior-posterior diameter of the chest (B). We performed these measurements at the 5th and 7th rib levels, and then averaged these measurements. We also measured the distance from the back to where the LTN enters SAM at the 4th, 5th, and 6th ribs. Results Analysis of the obtained data showed that the mean distance from the back to the anterior border of LDM at the 5th rib was 7.55 cm (5.65 – 10.85 cm) and at the 7th rib was 7.60 cm (5.35– 10.35 cm). Mean distance from the back to the anterior LDM border in both 5th and 7th ribs combined was 7.58 cm (5.50 – 1.06 cm). The mean anterior-posterior diameter of the chest wall at the fifth rib was 21.45 cm (18.55 – 24.75 cm). The mean A/B ratio (that is the ratio between the distance from the back to the anterior LDM border in comparison to the anterior-posterior chest diameter) was 0.4 with a standard deviation of +/- 0.1 (range 0.27-0.45). The LTN was running anterior to the LDM border at the 4th rib level, and posterior to the LDM border at the 5th and 6th ribs level. The LTN entered the SAM at the 4th rib level in 6.6%, at the 5th rib in 46.6% and at the 6th rib in 46.6% of cadavers. Discussion Intermuscular technique for S-ICD implantation is recommended as the preferred procedural approach. In our postmortem study, the anterior LDM border was variable but posterior to the mid-axillary line with a variable A/B ratio of 0.27 – 0.45. Our study also demonstrates the proximity of the long thoracic nerve (LTN) in comparison to the anterior LDM border. Caution should be taken when implanting S-ICD devices to avoid LTN injury.