In this appeal from a sentence of imprisonment imposed following convictions for robbery, theft and criminal conspiracy, Michael Edwin Johnson’s principal contention is that he was not tried within the time constraints of Pa.R.Crim.P. 1100(e)(1). Finding no merit in this contention or in any of the arguments advanced by appellant for a new trial,1 we affirm.
Johnson was arrested on January 4, 1983. His trial began on August 1, 1983. However, on August 2, 1983, a mistrial was declared because the jury was unable to agree upon a verdict. On December 20, 1983, after hearing, the trial court granted a timely request by the Commonwealth for an extension of time under Rule 1100 because the victim, Lyle Reynolds, had been ill and unavailable for trial when the case had been scheduled for trial in November. On February 21, 1984, another extension was granted because the victim was still ill. On March 6 and 7, 1984, *358within the extension allowed by the court, appellant was tried by jury and convicted.
Appellant argues that the trial court erred in granting the several Commonwealth requests for extensions. He contends that at both hearings the court improperly allowed hearsay evidence of the victim’s illness. In the absence of this hearsay, he suggests, the Commonwealth failed to prove that it was unable to commence trial within the prescribed period by the exercise of due diligence.
At the first extension hearing, Trooper James Anthony was the only witness to testify. He testified that he had been in contact with the victim, Lyle Reynolds, and had been told that he was ill and could not appear for trial. (N.T. 12/20/83 at 2, 4). Trooper Anthony testified that he had also gone to the office of Reynolds’ physician and had obtained letters, signed by the doctor, confirming that Reynolds was ill and could not appear for trial. Defense counsel objected to this testimony on grounds that it was hearsay. (N.T. 12/20/83 at 3). The court allowed Trooper Anthony to testify to what the letters said and admitted the letters into evidence as business records. (N.T. 12/20/83 at 5-6, 7). Appellant argues that Trooper Anthony’s testimony and the doctor’s letters were hearsay and should not have been received.
At the second hearing, Trooper Anthony testified that he had again spoken to Reynolds, who told him that he was still ill and unable to attend a trial. The trooper testified that he again went to the doctor’s office and obtained a letter, signed by the doctor, stating that Reynolds was ill and unable to appear. This time the court ruled that the letter was inadmissible as hearsay. (N.T. 2/21/84 at 6). Nevertheless, the extension was granted.
The Commonwealth had the burden of proving the-exercise of due diligence by a preponderance of the evidence. See: Commonwealth v. Ehredt, 485 Pa. 191, 194, 401 A.2d 358, 360 (1979); Commonwealth v. Bulling, 331 *359Pa.Super. 84, 90, 480 A.2d 254, 257 (1984); Commonwealth v. Lamb, 309 Pa.Super. 415, 423, 455 A.2d 678, 682 (1983).
[T]he due diligence required of the prosecutor by Rule 1100 has been interpreted to mean that the Commonwealth must exert reasonable efforts to provide for the trial to commence within [the prescribed period]. “The test in determining whether the Commonwealth acted with due diligence is one of reasonableness under the circumstances.”
Commonwealth v. Dancy, 317 Pa.Super. 578, 582, 464 A.2d 473, 475 (1983), quoting Commonwealth v. Wroten, 305 Pa.Super. 340, 345, 451 A.2d 678, 681 (1982) (emphasis in original). See also: Commonwealth v. Tann, 298 Pa.Super. 505, 507-508, 444 A.2d 1297, 1298 (1982); Commonwealth v. Long, 288 Pa.Super. 414, 419, 432 A.2d 228, 231 (1981).
Appellant is correct when he argues that the letters from the doctor were inadmissible to prove the truth of the facts recited therein. Writing letters to district attorneys is not a part of the ordinary course of a physician’s business. Therefore, the letters in question did not qualify as business records and should not have been received as substantive evidence of the victim’s illness. See: 42 Pa.C.S. § 6108. Cf. Commonwealth v. Garcia, 478 Pa. 406, 426, 387 A.2d 46, 56 (1978) (letter written by superintendent of mental hospital to court not a business record because writing letters to judges not done by hospital in ordinary course of business).
However, the issue in this case was not primarily the truth of the victim’s assertion and the doctor’s confirmation that the victim had been ill but whether the Commonwealth had exercised due diligence to commence trial within the time allowed by Rule 1100. With respect to this issue, it was relevant and proper to show that Trooper Anthony had attempted to have Reynolds present for trial and had been told both by Reynolds and his physician that Reynolds could not testify at trial because of illness. The statements made by Reynolds and his physician were admissible, not to show *360the truth of the statements made but to show that the Commonwealth had exercised due diligence. The statements were admissible to show that the Commonwealth had been unable to produce Reynolds for trial within 120 days after the prior trial had ended in a mistrial. Even if the facts recited by the witness and by his physician had been incorrect or even untrue, the witness’ statement and the physician’s letter were relevant to show that the Commonwealth’s failure to commence trial in a timely manner was not attributable to a failure to exercise due diligence.
By the use of this evidence, the Commonwealth was able to prove that it could not commence trial within 120 days despite its exercise of due diligence. Its efforts to have the victim, an essential witness, present for trial were prevented by his statement that he was ill and could not appear. The Commonwealth did not rest upon the assertion of the witness, however, but went to the witness’ physician in order to verify such illness. Only after confirmation by the witness’ physician did the Commonwealth seek an extension of time within which to commence trial. The trial court, on the basis of this evidence, could properly grant the several Commonwealth requests for extensions. The Commonwealth’s failure to issue a subpoena for Reynolds after he had alleged illness did not, in view of the circumstances of this case, suggest a lack of due diligence. See: Commonwealth v. Dancy, supra 317 Pa.Super. at 585, 464 A.2d at 477.
Appellant argues that even if Reynolds had been unavailable for trial, trial should have proceeded. Reynolds was not an essential witness, appellant argues, because the Commonwealth, in the event of his unavailability, could have used a transcript of the testimony which he gave at the first trial. The standard of due diligence, however, requires only that reasonable efforts be used by the Commonwealth to commence trial within the time allowed therefor. Numerous decisions have held that when witnesses become unavailable toward the end of the Rule 1100 period — whether because of illness, vacation or some other *361reason — the Commonwealth is entitled to an extension. See: Commonwealth v. Burke, 344 Pa.Super. 288, 496 A.2d 799 (1985); Commonwealth v. Williams, 317 Pa.Super. 456, 464 A.2d 411 (1983); Commonwealth v. Williams, 310 Pa.Super. 501, 456 A.2d 1047 (1983); Commonwealth v. Sharp, 287 Pa.Super. 314, 430 A.2d 302 (1981); Commonwealth v. Sinor, 264 Pa.Super. 178, 183-184 n. 5, 399 A.2d 724, 727-728 n. 5 (1979). Rule 1100 was not intended to require the Commonwealth to exercise extraordinary efforts to commence trial within the time constraints of Rule 1100. The standard is reasonable diligence. The Commonwealth’s evidence showed that trial was not commenced because of the witness’ representation that he was ill. This had been confirmed by his physician. Under these circumstances, the Commonwealth’s decision to wait until the witness could appear personally and testify in the presence of the jury was not equivalent to a lack of due diligence. Rule 1100, the Supreme Court has said, “ ‘ “serves two equally important functions: (1) the protection of the accused’s speedy trial rights, and (2) the protection of society.” Commonwealth v. Brocklehurst, 491 Pa. 151, [153— 154], 420 A.2d 385, 387 (1980); Commonwealth v. Hamilton, 449 Pa. 297, 297 A.2d 127 (1972)____ The administrative mandate of Rule 1100 certainly was not designed to insulate the criminally accused from good faith prosecution delayed through no fault of the Commonwealth.’ ” Commonwealth v. Crowley, 502 Pa. 393, 399, 466 A.2d 1009, 1012 (1983), quoting Commonwealth v. Genovese, 493 Pa. 65, 69-70, 425 A.2d 367, 369-370 (1981). See also: Commonwealth v. Hamm, 325 Pa.Super. 401, 416, 473 A.2d 128, 136 (1984). Because the Commonwealth’s inability to begin trial within 120 days of the prior mistrial was not caused by a lack of due diligence on the part of the Commonwealth, the trial court could properly extend the time for trial.
The judgment of sentence is affirmed.
SPAETH, President Judge, files a concurring and dissenting opinion.. These arguments are that the verdict was against the weight of the evidence; that the trial court erred in permitting rebuttal evidence to contradict appellant’s testimony; that the prosecutor was guilty of misconduct; and that the trial court’s jury instructions contained error. They have been fully discussed and correctly decided by the trial court and require no further discussion in this opinion.