(specially concurring).
While I am in full accord with the conclusion reached by the majority, I wish to add my own observations on some of the issues presented in the cause under review.
*593The fact that petitioner was the surviving spouse of the deceased employee did not of itself operate to render her incompetent as a witness in the proceeding. 12 O.S.1961 § 385, subdiv. 3; Rigdon & Bruen Oil Co. et al. v. Beerman et al., Okl., 346 P.2d 169, 171. Her testimony concerning decedent’s actions on the day of his death tends to shed light upon the cause of the fatality and was clearly admissible. Decedent’s statements, made to petitioner on that date, relate to his physical efforts and activities and do have a bearing upon the cause of death. They were also admissible if part of res gestae. The duty of ascertaining whether such statements came within the res gestae rested upon the trial judge. Admissibility of statements as a part of res gestae is largely controlled by the facts and circumstances of each case, and the matter should, in a great measure, be left to the determination of the trial court. Huffman v. Gaylor, Okl., 267 P.2d 564. It is not clear here whether petitioner’s proffered testimony was rejected due to erroneous belief that she was not a competent witness, or because the statements sought to be introduced were deemed to lie beyond the limits of the res gestae rule. I am, therefore, convinced that the Industrial Court should be instructed to determine, on rehearing of the claim, whether or not decedent’s statements were a part of res gestae, and if they be so found, to receive them in evidence.
I agree that compensability in cases of this sort does not depend on the factum of a “severe” strain or “unusual” exertion. The controlling issue under inquiry is whether competent medical evidence discloses that death was causally related to the work done by decedent in the course of his employment. While not an indispensable element in the chain of evidence, proof of an unusual or unaccustomed effort of labor is nonetheless highly relevant, because it serves to aid in demonstrating that the heart injury, be it disabling or fatal, did not result from some spontaneous or natural cause, but was at-tnbutable to work-connected strain or exertion. Black, Sivalls & Bryson, Inc. v. Coley, Okl., 367 P.2d 1017; Farmers Cooperative Association et al. v. Madden et al., Okl., 356 P.2d 741.