Minimally invasive cardiac surgery requires a learning period before the advantages of the method can be demonstrated. We report the progress of our results over 21 consecutive months. 27 patients were considered for minimally invasive coronary bypass via a small thoracotomy. We compare the results of four consecutive groups corresponding to an initial period (July-December 1997; n = 7; 66.8 +/- 8.9 years), an intermediate period (January-June 1998; n = 4; 48.1 +/- 11.2 years), an advanced period (July-December 1998; n = 7; 62.9 +/- 7.0 years) and a current period (January-March 1999; n = 7; 59.3 +/- 10.9 years). 2 patients were converted to sternotomy during the first year of experience. The operating time was reduced from 124 +/- 14 min and 118 +/- 20 min during the initial and intermediate periods to 99 +/- 18 and 98 +/- 18 min during the last two periods. The ICU stay was 2.6 +/- 1.1 days during the initial period and diminished respectively to 1.5 +/- 0.6, 1.7 +/- 0.8 and 1.6 +/- 0.5 days during the intermediate, advanced and current periods. The postoperative hospital stay was reduced from 9.0 +/- 1.4 days to 6.3 +/- 4.6, 5.2 +/- 1.7 and 5.9 +/- 1.5 days respectively. The benefits of minimally invasive coronary bypass were estimated by comparing the results of the last two periods with those of patients operated on through a sternotomy, on a beating heart (n = 12; 62.6 +/- 8.2) or under CPB (n = 81; 63.0 +/- 8.5). In these situations, operative time was 144 +/- 41 min and 180 +/- 35 min respectively. The ICU stay was 1.5 +/- 0.6 and 2.2 +/- 0.9 days, and the postoperative hospital stay was 7.5 +/- 2.8 and 8.6 +/- 3.0 days. We conclude that a learning period is necessary before the real benefits of the minimally invasive approach to coronary disease can be demonstrated. This method will soon replace traditional sternotomy in certain indications.