After baseline recordings of contractile function, the investigators will assign 2 trabeculae of each patient to either a stimulus for (1) ischemic preconditioning (IP) or (2) no IP. Subsequently, the trabeculae will be exposed to 90 min of ischemia, followed by 120 minutes of recovery. The investigators will measure the recovery of contractile function in both trabeculae.

This experiment serves as a positive control, to ensure that our model is still working properly.

In the next patients, a similar ischemia-reperfusion experiment will be performed, but now the 2 trabeculae will be randomized to pretreatment with eplerenone or DMSO. The percentage recovery (compared to baseline) of contractile force of the trabeculae at the end of reperfusion will serve as the primary endpoint.

eplerenone administered ex vivo (to the organ bath in which human atrial tissue is exposed)

The recovery of contractile function (% of baseline) in human myocardial tissue after simulated ischemia and reperfusion in 2 trabeculae will be compared: 1 of the trabeculae will be exposed to eplerenone, the other to vehicle.

We will use the experimental set up as described by Speechly-Dick et al. with small modifications to allow simultaneous measurement of 2 trabeculae from 1 patient. The two trabeculae will be dissected and vertically suspended in an organ bath and linked to a force transducer. During electrical field stimulation, we will calculate the developed force (difference between maximal tension during contraction and minimal tension during relaxation), maximal speed of tension development during contraction and maximal speed of tension during relaxation. We will average these parameters for baseline, and during the experiment. Functional recovery will be expressed as a percentage of baseline.