This study evaluates the feasibility and safety of a 6Fr hydrodynamic thrombectomy catheter, the Hydrolyser, in native coronary arteries and aortocoronary bypass grafts. With use of a conventional contrast injector, saline solution is injected into the narrow lumen of the catheter which makes a 180 degrees bend at the tip. The resultant high-velocity jet (150 km/hour) is directed over a sidehole near the tip into a wide exhaust lumen. As a consequence of the Venturi effect, thrombus is sucked into that sidehole, fragmented, and removed through the wide exhaust lumen into a collection bag. Thirty-one thrombotic lesions were treated in 31 patients. The culprit vessel was a venous graft in 21 patients (15 with Thrombolysis in Myocardial Infarction Trial [TIMI] grade 0 or 1 flow) and a coronary artery in 11 patients (9 with grade 0 or 1 flow). Twenty-six patients had angina New York Heart Association functional class III or IV heart failure and 5 an acute myocardial infarction. In 26 patients, Hydrolyser therapy was the primary treatment, whereas in 5 patients coronary angioplasty preceded Hydrolyser therapy. In 1 patient the Hydrolyser could not reach the lesion. Thrombus was removed in 29 of the 31 patients. Successful reperfusion (TIMI grade 2 or 3 flow) by Hydrolyser therapy alone was achieved in 14 of the 24 patients with TIMI grade 0 or 1 flow before the procedure. Adjunctive therapy (coronary angioplasty, stent, or thrombolysis) was performed in 28 of the 31 patients. At the end of the total procedure 24 patients had TIMI grade 3 flow. Distal embolization during thrombectomy occurred in 2 patients, which led to a non-Q-wave infarction in 1. No patient died or needed emergency coronary bypass due to the Hydrolyser procedure. Thus, thrombectomy using the 6Fr Hydrolyser is feasible and was performed safely in 31 patients.