In patients with spontaneous coronary artery dissection (SCAD), many continue to have ongoing signs and symptoms of ischemia after the dissection has healed. Further, 1 in 5 women will experience recurrent SCAD in long-term follow-up. To date, no study has investigated the pathophysiologic mechanism behind ongoing symptoms or recurrence of SCAD, but microvascular coronary dysfunction (MCD) has been suggested. Coronary reactivity testing (CRT) is an invasive procedure currently being done in MCD patients as the gold standard technique. In particular, a coronary flow reserve (CFR) < 2.5 has been shown to be both diagnostic of the condition and prognostic of a 2 fold increased risk of cardiac events. Please see below for a detailed description of CRT. In brief, a dual temperature and pressure sensor tipped wire by Radi Medical Systems (St Jude Medical, St Paul, MN) will be placed into the dissected and non-dissected coronary arteries of the patient. This will measure CFR by thermodilution and will also allow the measurement of the index of microcirculatory resistance (IMR). IMR has been found to correlate well with true microvascular resistance.