Pericardial effusion can be a life-threatening complication in children after cardiac surgery. Percutaneous pericardiocentesis is associated with rare, but serious complications. This retrospective study describes our experience with a novel, long-axis in-plane real-time ultrasound (US)-guided technique for postoperative pericardial effusion drainage in small children. Ten out of sixteen procedures were performed within 14 days of cardiac surgery at a median postoperative day 12 (IQR 2, 99). Median age was 2.7 months (IQR 0.4124) and weight 4.5 kg (IQR 2.5, 41.6). All but one procedure required a single attempt. Fourteen out of sixteen procedures had subxiphoid approach, and two were apical. Median initial drainage was 9 mL/kg (IQR 4.5, 27). Fifty percent of effusions were serous, 25 % chylous, and the remainder bloody. There were no reported complications. This study demonstrates a novel, long-axis pericardiocentesis technique that allows for an easy and safe needle entry into the pericardial space for small children in the early postoperative period.