A number of studies have used 2,3-butanedione monoxime (BDM) to avoid myocardial damage when small muscle preparations were cut from large hearts. The present study investigates the mechanical and energetic effects of varying muscle cross-sectional area (CSA) by dissection in physiological saline containing BDM. By use of adult rat hearts, three muscle groups were obtained: whole left ventricular papillary muscles (Whole) and left ventricular papillary muscles split longitudinally in the presence of 30 mM BDM, with removal of approximately 10% (BDMSP1) or 40-50% (BDMSP2) of the muscle (5 animals in each group). The isolated muscle preparations were studied at 27 degrees C and stimulated at 0.167 Hz. The Whole and BDMSP1 preparations had comparable CSAs; in isotonically contracting muscles working against a range of afterloads, work, enthalpy (energy use), and mechanical efficiency (work/enthalpy x 100%) were similar for the two groups. In addition, isometric performance [e.g., developed stress (force/CSA), length-tension relationship, and contraction time course] was also similar for the two groups. The thinner BDMSP2 preparations showed an enhanced mechanical performance compared with the Whole and BDMSP1 groups. This outcome was in accordance with data in the literature documenting a negative correlation between stress and CSA. The results suggest that BDM-split and intact papillary muscles of similar CSA have comparable energetic and mechanical properties.