Objective: We investigated the feasibility and short-term effects of a novel procedure to create intramyocardial channels by means of high frequency (HF) ablation in a rabbit in vivo model. Methods: A flexible catheter ending in a cylindrical electrode (diameter 0.7 mm) with a sharpened tip was used for HF energy application following transmyocardial insertion. Power-controlled or energy-controlled energy applications were performed in 16 anesthetized rabbits after thoracotomy with a follow-up for 3 h. Assessment of myocardial channels and the necrotic zone was performed by morphometric quantification in serial sections. The ferret diameter was used to compare channel dimensions and the extent of necrosis. Results: Thirty-nine power-controlled and 54 temperature-controlled HF applications were performed. The shape of identified channels was round in 71% and 69% had a lumen patency of ≥2/3 of the channel. Ferret diameter of the channels was 414 ± 180 μm and of the necrotic zone 3,558 ± 1,200 μm. In temperature-controlled applications, channel dimensions were strongly influenced by the maximum tissue temperature and the duration of energy delivery (T<sub>max</sub>: p = 0.0006; duration: p = 0.003). Channel and necrosis dimensions correlated better with biometric parameters in temperature-controlled compared with power-controlled applications. Conclusion: Mechanically created transmyocardial channels can be stabilized by HF heating of the surrounding tissue. A high percentage of these channels remain patent. The channel dimensions are closely correlated with maximum temperature and duration of energy delivery in a temperature-controlled application mode.