ALJ allowed to rely on medical advisor's opinion in the face of contradictory findings. Claimant's burden at Step 4 includes proving the particular demands of past work that she cannot perform. Secretary allowed to rely on medical advisor's opinion that the treadmill exercise test was acceptable. Treating physician's opinion not to be accorded greater weight.

Cardiac and mental impairments. Although the Secretary is not bound by a psychiatrist's "sweeping conclusion" as to disability, when uncontroverted evidence exists as to mental impairment, the Secretary should assess the impact of the alleged mental impairment on the claimant's ability to engage in SGA. Grid cannot be applied if claimant's nonexertional impairment significantly affects claimant's ability to perform the full range of jobs requiring medium or lesser work. Secretary must use other means, such as evidence procured from vocational experts, to meet her burden of proving the availability of jobs in the national economy that claimant can perform. None of the physicians who examined claimant provided any medical findings concerning the impact of his heart condition on his residual functional capacity. Neither the Appeals Council nor the court is qualified to make this medical judgment about residual functional capacity based solely on bare medical findings as to claimant's heart condition. The claimant has the burden of showing disability serious enough to prevent him from working at his former jobs. The burden then shifts to the Secretary to show the existence of other jobs in the national economy that the claimant can nonetheless perform. Where no examining physician has provided "any medical findings concerning the impact of [claimant's] heart condition or his residual functional capacity... [n]either the Appeals Council nor this court is qualified to make this medical judgment about residual functional capacity based solely on bare medical findings as to claimant's heart condition." None of the physicians who examined claimant provided any medical findings concerning the impact of his heart condition on his residual functional capacity.

At Step 4, the ALJ is entitled to credit the claimant's own description of her past work and her functional limitations, but the ALJ has some burden independently to develop the record. Citing Santiago, 944 F.2d 1 (1st Cir. 1991). Remand. Illegibility of non-trivial parts of medical record, combined with identifiable diagnoses and symptoms indicating more than a mild impairment, alerted ALJ to need for expert guidance regarding the extent of the claimant's RFC to perform her past employment. Case remanded. With a few exceptions, an ALJ, as a lay person, is not qualified to interpret raw data in a medical record. Where claimant sufficiently put her inability to perform her past work in issue, the ALJ must measure the claimant's capabilities, and ordinarily an expert's RFC evaluation is essential unless the extent of functional loss, and its effect on job performance, would be apparent even to a lay person. Ventricular tachycardia, frequent PVCs, sinus tachycardia, arterial hypertension